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Hill! 



POWER PLANT TESTING 



Published by the 

McGrow-Hill BookCompany 

N<ew Yoirlk. 

6ucce5sora to the Dock. Departments of the 

McGraw Publishing Company Hill Publishing* Company 

Publishers of Books for 
Electrical World The Engineering and Mining' Journal 

Engineering Record American Machinist 

Electric Railway Journal Coal Age 

Metallurgical and Chemical Engineering Power 



POWER PLANT 
TESTING 



A MANUAL OF TESTING ENGINES, TURBINES, BOILERS, 

PUMPS, REFRIGERATING MACHINERY, FANS, FUELS, 

LUBRICANTS, MATERIALS OF CONSTRUCTION, ETC. 



BY 

JAMES AMBROSE MOYER, S.B., A.M. 

Member American Society of Mechanical Engineers, Mitglied des Vereines deutscher Ingenieure, 

Membre titulaire Association Internationale du Froid, Member of the Franklin 

Institute, Society of Automobile Engineers, American 

Institute of Electrical Engineers, etc. 

Professor of Mechanical Engineering in The Pennsylvania State College and in charge of 

Pennsylvania Engineering Experiment Station, formerly Engineer, Steam 

Turbine Department. General Electric Company, and Engineer, 

Westinghouse, Church, Kerr & Company 



SECOND EDITION 

REWKITTEN, ENLARGED AND ENTIRELY RESET 



McGRAW-HILL BOOK COMPANY, Inc. 
239 WEST 39TH STREET, NEW YORK 

6 BOUVERIE STREET, LONDON, E. C. 

1913 



T 5" i V* 
.Ml 
\ <\ \"5 



Copyright, 1911, 1913, by the 
McGRAW-HILL BOOK COMPANY, INC. 



Stanbopc iprcss 

H.GILSON COMPANY 
BOSTON, U.S.A. 



.': . 



A3516 3 



PREFACE TO FIRST EDITION 



In the preparation of this book the object in view has been primarily 
to give in a small volume, somewhat in detail, the generally approved 
methods of testing engines, turbines, boilers and the auxiliary machinery 
usually found in power plants, as well as to present more or less complete 
descriptions of the various kinds of apparatus used and the calibrations 
required for accurate testing. In addition to this subject-matter, chap- 
ters have been prepared on the testing of fuels, refrigerating and hydraulic 
machinery, as well as on the proper methods and the machinery to be 
used in making tests of the strength of the materials commonly used in 
the construction of buildings. 

As a book for students in laboratory courses it is intended particularly 
for use in large classes in which at the beginning of the laboratory periods 
it is necessary to begin at the same time a number of different experi- 
ments and tests. On this account care has been taken to state as clearly 
as possible the descriptions of the apparatus to be used and the precau- 
tions to be observed to secure accuracy in the results. Students should 
be expected, however, to rely to some extent on their own initiative. 

In most respects the book is probably complete enough in descriptive 
matter and in general instructions so that very little lecture-room work 
is needed for at least elementary courses. It is the author's opinion 
that students in experimental engineering laboratories should not re- 
ceive a great deal of assistance in planning and conducting tests. Some- 
time they must learn to be resourceful and independent of the "school" 
type of instruction and obviously the sooner this is appreciated by both 
instructors and students the greater will be the benefits. At least for 
very small classes the better plan is the one advocated years ago by a 
famous educator, that students working in laboratories when assigned the 
work of testing a machine, a new type of aeroplane engine, for example, 
should have very simple instructions such as: "Make tests of this new 
type of engine, find out what you can about it and report your results." 
It is to be hoped that the particular method of teaching in laboratories, 
known familiarly as "feeding with a spoon," has disappeared in present- 
day instruction in technical schools and colleges. 

Quite a large part of the training required for one to become accurate 
and reliable in the work of observing and interpreting the results of 



vi PREFACE TO FIRST EDITION 

tests of machinery consists in becoming familiar with the details of the 
adjustment and calibration of the various instruments, so that they 
may be used intelligently. 

Although in the arrangement of the chapters the use of the book by 
students was given the most careful consideration, yet as a whole the 
needs of the "practical" man were not lost sight of, and it is hoped that 
the author's experience when working with this group of readers in testing 
both large and small power plants has helped to make the book inter- 
esting and helpful to them. The book is intended to be also a manual 
giving useful information in a more or less limited way to those profes- 
sional engineers having the advantages of a technical training, but who 
are not thoroughly familiar with the most up-to-date methods of testing. 

In many cases not nearly all the results that should be calculated to 
make up a complete report are mentioned. It is the opinion of the 
author that in a text-book it is desirable that no more than very general 
instruction should be given regarding the conduct of the test, the quan- 
tities to be calculated, and the form and tabulations expected in a report. 
Such details should be left in the hands of the instructor. Because the 
size of the book was limited it was necessary to omit explanations of the 
methods of calculating many interesting and more or less applicable re- 
sults from tests. In the more extended courses it is believed that the 
instructors can readily fill in these omissions. 

The author is particularly indebted in the preparation of this book 
to Dean M. E. Cooley and Professor J. R. Allen, of the University of 
Michigan; Professor L. S. Marks, of Harvard University; Professor 
H. W. Spangler, of the University of Pennsylvania; Dean W. F. M. 
Goss, of the University of Illinois; Professor C. H. Peabody, of the Massa- 
chusetts Institute of Technology; Professor L. V. Ludy, of Purdue 
University; Professor A. M. Greene, of Rensselaer Polytechnic Insti- 
tute; Professor C. C. Lorentzen, of New York University; Professor E. 
J. Fermier, of the Mechanical and Agricultural College of Texas; Professor 
E. A. Fessenden, of the University of Missouri; Professor F. H. Sib- 
ley, of the University of Alabama; Dr. C. P. Steinmetz and Mr. Rich- 
ard H. Rice, of the General Electric Company; Mr. H. R. Kent, Vice- 
president, Westinghouse, Church, Kerr & Company; Mr. J. R. Bibbins, 
of the Arnold Company; Mr. R. A. Smart, of the Westinghouse Machine 
Company; Mr. St. John Chilton, of the Allis-Chalmers Company; and 
Mr. G. E. Wallis, New York City. 

J. A. MOYER. 

Ann Akbor, Michigan. 
August, 1911. 



PREFACE TO SECOND EDITION 



On account of the very great extension of experimental work in engi- 
neering laboratories, and the great demand for a suitable manual of small 
size and clearly written for the use of students, this book has been largely 
rewritten and a number of new sections have been added to make it more 
adaptable to the large number of engineering schools using it as a text. 

The latest revisions (1912) of the standard codes adopted by the Power 
Test Committee of the American Society of Mechanical Engineers have 
been incorporated practically without abridgment to make the book 
thoroughly up-to-date. 

Outlines of a series of tests arranged to suit as nearly as possible a 
large number of American technical schools have been added to assist 
both the instructor and the student. By the judicious use of these out- 
lines at least fifty per cent of the time of an instructor can be saved; 
the general efficiency of the courses will be improved; and the predomi- 
nating idea underlying the original conception of this book as stated in 
the third paragraph of the first preface is more nearly realized. 

The most obvious weakness of laboratory instruction to be observed, 
particularly when large classes are the rule, is that students have assim- 
ilated with thoroughness very little of what has been taught. The prin- 
cipal difficulty is that the students have been permitted to depend too 
much on laboratory notes prepared by the instructors, which are com- 
plete enough for the particular test in hand but are not sufficiently general 
in the discussions. It is the general conclusion of many who have inves- 
tigated, that the only way out of this difficulty is to require written 
recitations, say once every week or every other week for about a half 
hour to review the general subject matter and the exact details of the 
methods used in making the tests. 

It is a good plan also for the instructor to require students to make 
approximate calculations of the principal results of each test, under his 
personal supervision, before they report for making the accurate calcula- 
tions going into their reports. In this connection the instructor should 
feel it his duty to be certain that the students understand the methods 
of obtaining the important results before a laboratory test is started. 
There is no better place than an engineering laboratory to impress the 
importance of rough calculating, plotting, and checking of results than 



viii PREFACE TO SECOND EDITION 

such work done while a test is in progress. One-half of the data gen- 
erally collected by undergraduates doing "thesis work" is practically 
valueless because the importance of calculating roughly for final and im- 
portant results is not properly appreciated. If such work is not to be 
done well it might better not be done at all. 

In the preparation of this edition the author is particularly indebted 
to Dean F. P. Anderson, Univ. of Ky.; Mr. G. H. Barrus, Boston, Mass.; 
Prof. J. P. Calderwood, Pa. State Col.; Prof. F. E. Cardullo, New Hamp- 
shire Col.; Prof. R. C. Carpenter, Miss. A. & M. Col.; Prof. A. G. 
Christie, Univ. of Wis.; Prof. A. W. Cole, Purdue Univ.; Prof. J. E. 
Emswiler and Prof. C. H. Fessenden, Univ. of Mich.; Prof. S. H. Graf, 
Oregon State Col.; President I. N. Hollis, Worcester Poly. Inst.; Prof. 
A. C. Jewett, Univ. of Maine; Prof. W. H. Kavanaugh, Univ. of Minn.; 
Prof. W. H. Kenerson, Brown Univ.; Prof. E. W. Kerr, La. State Univ.; 
Prof. E. H. Lockwood, Yale Univ.; Mr. F. R. Low, Editor of Power; 
Prof. L. S. Marks, Harvard Univ.; Prof. P. B. Otis, Col. Sch. of 
Mines; Prof. A. A. Potter, Kans. State Col.; Prof. F. L. Pryor, Stevens 
Inst, of Tech.; Mr. W. W. F. Pullen, London, Eng.; Prof. C. R. Richards, 
Univ. of 111.; Prof. R. Royds, Glasgow (Scotland) Tech. Col.; Sir H. R. 
Sankey, Ealing, Eng.; Prof., J. C. Smallwood, Syracuse Univ.; Prof. 
C. J. Til den, Johns Hopkins Univ.; Prof. A. F. Walker, Univ. of Kansas; 
Prof. H. C. Weaver, Univ. of Texas; Prof. A. C. Wescott, Univ. of Mo.; 
and Prof. G. S. Wilson, Univ. of Washington. 

J. A. MOYER. 

State College, Pennsylvania, 
August, 1913. 



INTRODUCTION 



Tests of the machinery in a power plant are usually made to deter- 
mine the capacity and efficiencies of its various units when operating 
under certain definite conditions. In recent engineering practice manu- 
facturers and contractors are generally required to make certain estimates 
and guarantees of the capacity and efficiency of the various kinds of 
machinery supplied. This is exactly equivalent, in other words, to 
agreeing to provide for doing a given unit of work under specified condi- 
tions at a definite cost. The purchaser, on the other hand, for his pro- 
tection, finds it necessary to determine from the results of reliable tests 
whether the " guarantees " can be obtained. Obviously, then, the im- 
portance of knowing how to make careful and reliable tests, of which the 
results will not be questioned, cannot be overestimated. 

Tests of power plants as a whole are also necessary and should be made 
from time to time in order to determine what results can be obtained 
from an economic viewpoint when operating under the existing condi- 
tions; and also for finding out what saving can be obtained by changes 
in the operating conditions or by the installation of more efficient auxiliary 
machinery. From the viewpoint of determining whether or not it is 
economical to replace old equipment with new, tests of old installations 
are relatively more important than those of newer ones, because usually 
it is out of the question to' relegate practically new machinery to the 
scrap-heap. The greatest importance of such tests is due, however, to 
the fact that they show how nearly the existing conditions of operation 
conform to those of standard engineering practice, and to those obtained 
in other plants operating with the greatest success. 

Practice tests in the laboratory are intended to show to students by 
actual experience the best methods for investigating the problems arising 
in the operation of plants, how to work out in a practical way the doubt- 
ful points in designing and constructing machinery, and, above all, to 
think accurately and systematically in such matters. 

Procedure for making accurate tests may be stated as follows: 

1. Procuring a suitable standard testing equipment. Any instruments 
and apparatus not well known to engineers generally and which are of 
doubtful accuracy or sensitiveness should always be avoided. Remem- 
ber that a single element of uncertainty may vitiate the acceptance of 
the results of a test of otherwise undoubted accuracy. 



x INTRODUCTION 

2. Careful calibrating of instruments before a test, so that the great- 
est possible errors of the tests are definitely known and that proper allow- 
ance can be made in the results. 

3. Systematic recording of observations. 

4. Recalibrating of instruments after a test to determine whether 
there have been any changes in their accuracy. 

5. Preparing of a report embodying data, results and conclusions. 

6. Tabulating and plotting on cross-section paper the important re- 
sults. This plotting is not only for the purpose of showing the results 
graphically, but also for the purpose of providing a check or a method 
of eliminating errors in observations or in calculations. The skill of an 
engineer in testing is shown, more than in any other way, by his ability 
to check results. If after applying various checks, usually by means 
of plotted curves, the results for varying conditions are found to agree, 
the engineer is able to tell definitely whether or not his tests are reliable. 



CONTENTS 

PAGE 

Introduction ix 

I. Measurement op Pressure 1 

(1) Manometer or U-tubes 1 

(2) Barometers 4 

(3) Bourdon Gage 8 

(4) Diaphragm Gage 11 

(5) Vacuum Gage 12 

(6) Recording Gage 12 

(7) Calibration of Pressure Gages 15 

Dead-weight Gage Testers 17 

Mercury Columns 19 

(8) Calibration of Vacuum Gages 22 

(9) Calibration of Low-pressure Gages 22 

(10) Draft Gages 24 

II. Measurement op Temperature 28 

(1) Mercurial Thermometer 28 

(2) Alcohol Thermometer 29 

(3) Calibration of Thermometers 29 

Compared with Standard Thermometer 31 

Compared with Temperature of Steam 34 

(4) Corrections for Stem Exposure 36 

(5) Recording Thermometers 39 

(6) Pyrometers 41 

a. Thermo-electric 41 

b. Electric Resistance 44 

c. Mechanical 45 

d. Radiation 47 

e. Optical 50 

/. Calorimetric 51 

(7) Seger Cones 52 

III. Determination op Moisture in Steam ' 55 

(1) Throttling Calorimeter 55 

(2) Separating Calorimeter 63 

(3) Combined Separating and Throttling Calorimeter for Low-pressure 

Steam 65 

(4) Electric Calorimeter 69 

(5) Barrel Calorimeter 70 

(6) Calibration of Calorimeters 73 

IV. Measurement op Areas 74 

(1) Planimeters 75 

a. Polar 76 

b. Coffin 81 

c. Roller 85 

(2) Testing of Planimeters 86 

(3) Durand-Bristol Integrating Instrument 87 

xi 



ii CONTENTS 

PAGE 

V. Engine Indicators and Reducing Motions 92 

(1) Indicators 92 

a. Watt 93 

b. Thompson 93 

c. Crosby 95 

1. Inside Spring 96 

2. Outside Spring 98 

d. Star Brass 99 

e. Tabor 99 

/. Bachelder 102 

g. Cooley-Hill Continuous Indicator 106 

h. Optical 108 

(2) Calibration of Indicator Springs 112 

(3) Tests of Drum Springs 120 

(4) Reducing Motions 121 

a. Pendulum Reducing Motions for Indicators 124 

b. Pantograph or Lazy-Tongs 126 

c. Reducing Wheels Attached to Indicators 132 

(5) Errors in Indicator Diagrams ' 136 

(6) Calculation of Indicated Horse Power 141 

(7) Indicated Horse Power of Rotary Engines 143 

(8) Speed Counters and Tachometers 144 

VI. Measurement of Power 147 

(1) Absorption Dynamometers 147 

a. Prony Brake 148 

b. Rope Brake 152 

c. Alden Dynamometer 155 

d. Water Brakes of Various Types 156 

(2) Electric Generators and Motors as Dynamometers 162 

(3) Transmission Dynamometers 164 

. Goss 164 

Differential 165 

Webber 167 

Emerson Power Scales 168 ' 

Flather 169 

(4) Torsion or Shaft Dynamometers 170 

a. Electric 173 

b. Optical 173 

c. Fluid Pressure (Kenerson's) 174 

(5) Accelerometer 174 

VII. Flow of Fluids 176 

(1) Air and Other Gases 176 

o. Meter 177 

b. Pitot Tube 178 

c. Anemometers 182 

d. Orifice 184 

e. Calorimetric Method 187 

(2) Steam — Wet, Dry, Saturated, and Superheated 189 

a. Orifice 189 

6. Pitot Tube Meters 191 

c. Orifice Meters 192 



CONTENTS xiii 

PAGE 

(3) Water 193 

a. Meters 194 

b. Automatic Weigher 196 

c. Venturimeter 199 

d. Orifice 201 

e. Weir 203 

/. Weir Meters 205 

VIII. Calorific Value of Fuels 210 

(1) Fuel Calorimeters 210 

a. Calculation of Water Equivalent 210 

6. Mahler 211 

c. Atwater 216 

d. Emerson 216 

e. Parr 217 

/. Carpenter 220 

g. Junkers 222 

(2) Calorific Value from Analysis 227 

(3) Proximate Analysis 228 

IX. Flue Gas Analysis 235 

(1) Sampling Bottles and Tubes 236 

(2) Fisher's "Orsat" Apparatus 241 

(3) Allen-Moyer Gas Apparatus 243 

(4) Hempel Gas Apparatus 245 

(5) Calculations 249 

a. Weight of Air 250 

6. Weight of Gases 251 

(6) Recording Apparatus for C0 2 252 

(7) Smoke Determinations 255 

X. Instructions Regarding Tests in General 258 

XL Boiler Testing 267 

A.S.M.E. Rules and Data Sheets 269 

XII. Steam Engine Testing 284 

(1) Mechanical Efficiency and Friction 284 

(2) Valve Setting 285 

a. Slide Value 285 

b. Corliss Valve 288 

(3) Clearance Tests 293 

(4) A.S.M.E. Rules and Data Sheets 294 

(5) Heat Data 302 

(6) Thermal Efficiency. . . ; 305 

(7) Rankine Cycle 308 

(8) Steam Consumption from Indicator Diagram 310 

(9) Willans Law 312 

XIII. Testing of Steam Turbines and Turbine Generators 315 

XIV. Methods for Correcting Steam Engine and Steam Turbine Tests 

to Standard Conditions 329 

XV. Tests of Complete Steam Power Plants 336 

XVI. Gas Engine and Producer Tests 341 

(1) Indicated and Brake Horse Power 341 

(2) Gas Engine Indicators 342 

(3) Measurement of Fuel 343 



xiv CONTENTS 

PAGE 

(4) A.S.M.E. Rules and Data Sheets for Gas Engines 345 

(5) Abnormal Indicator Diagrams . 350 

(6) Gas Producers 353 

(7) Capacity and Efficiency of Gas Producers 353 

(8) A.S.M.E. Rules for Data Sheets for Producers 354 

(9) Tests of Complete Gas Power Plants 362 

XVII. Tests of Ventilating Fans or Blowers and Air Compressors 364 

Humidity Determinations 368 

XVIII. Tests of Refrigerating Machines . 377 

(1) Compression System 378 

(2) Absorption System 385 

XIX. Tests of Hot-Air Engines 389 

XX. Tests of Hoists, Belts, Rope Drives, and Friction Wheels 391 

XXI. Tests of Lubricants 395 

XXII. Tests of Hydraulic Machinery 408 

(1) Belt-driven Feed Pumps ' 409 

(2) Steam Feed Pumps 410 

(3) Impulse Wheels 419 

(4) Water Turbines 422 

(5) Air Lifts 423 

(6) Hydraulic Rams 424 

(7) Pulsometers 426 

(8) Injectors 428 

XXIII. Tests of the Strength of Materials 431 

XXIV. Outlines of Suggested Tests 460 

Appendix 468 

(1) Steam Tables 468 

(2) Properties of Common Substances 473 

(3) Metric Conversion Table 473 

(4) Pressure Equivalents 474 

Index 475 



POWER PLANT TESTING 



CHAPTER I 



MEASUREMENT OF PRESSURE 





The simplest instrument used for measuring pressure is a glass tube 
bent into the shape of the letter U, as illustrated in Fig. i. When such 
a tube, called technically a manometer or U-tube, is 
partly filled with a liquid, usually water or mercury, 
and is connected at A by means of tubing to the ves- 
sel in which the pressure is desired, there will be 
observed a difference in the level of the liquid corre- 
sponding to the pressure. If the end of the tube at 
B is open to the atmosphere, then 
the difference in the level of the 
liquid in the two legs measured in 
inches, multiplied by the weight of 
a cubic inch of the liquid in pounds, 
gives the difference in pressure in 
pounds per square inch between that 
in the vessel and atmospheric pres- 
sure. When the level in the leg B 
is higher than in A then the pressure 
measured is greater than atmospheric and is called gage 
pressure to distinguish it from the other condition when 
the level in the leg A is higher than in B ; that is, when 
the pressure is less than atmospheric. In the latter 
case we speak of vacuum or negative pressure. 

As such instruments are usually constructed, a scale 
suitably graduated for measuring the difference be- 
tween the levels of the liquid in the tube is placed 
between the two legs, as shown in Fig. 2. Still another 
type is illustrated in Fig. 3. In a manometer of this 
kind one leg can be made very short if it is corre- 
spondingly large in diameter. If the scale is adjusted 
so that the level in the short leg is at the zero of the scale, then the 
level in the long leg will indicate directly inches of pressure or of vacuum 



Fig. 1. — A U-tube 
for measuring Pres- 
sures. 



Fig. 2. — Manom- 
eter or U-tube with. 
Graduated Scale. 



2 POWER PLANT TESTING 

as the case may be. A typical vacuum gage of the same kind is illus- 
trated in Fig. 4. The end of the tube corresponding to the short leg in 
Fig. 3 is shown at A. When manometers are to be used for pressure or 
vacuum measurements of steam, a condensation trap (B, Fig. 5) is often 
employed to prevent the passage of steam into the glass tube in which 
it would form a water column on the top of the mercury for which a cor- 
rection 1 would have to be made. To be effective the condensation trap 



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Fig. 4. 
Typical Mercury Vacuum 




B must always be partly filled 'with water. It must not however be 
allowed to become completely filled so as to discharge water through the 
pipe D joining the trap with the glass vacuum tube. A glass tube E, 
called technically a water gage, shows the level of the water in the trap 

1 Correction for water on the top of a mercury column is most conveniently made 
by dividing the length of the water column by the specific gravity of mercury (13.6) 
and adding this equivalent length to the mercury column on which the water rests. 



MEASUREMENT OF PRESSURE 3 

and should always be kept clean. Cock C is provided for draining off 
excess of condensation. 

The graduated scales on vacuum gages, like Figs. 3, 4, and 5, must be 
adjustable so that the zero can be made to coincide exactly with the 
level of the mercury when both legs are open to atmospheric pressure. 
Scales are usually arranged to be raised and lowered by turning a milled 
knob, like K in Fig. 5, which is connected by a screw thread to the scale. 
Vacuum gages, like Fig. 3, without ready means for adjustment cannot 
be arranged to indicate accurately vacuums that are varying, because 



.0.20 







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0.115 0.1 0.15 0.2 0.3 0.4 0.5 (i • 



Diameter of Tube in Inches. 
Fig. 6. — Curve of Capillarity Corrections for Mercury Columns. 

the measure of the vacuum is the difference in level between the columns 
in the two legs. Unless the area of the reservoir is very large; in all 
vacuum manometers either the scale must be shifted or the level in the 
reservoir changed for varying magnitudes of vacuum. 

Manometers or U-tubes of very small diameter when filled with mer- 
cury may be affected by capillarity to such an extent that in order to 
obtain the true height corresponding to the pressure, a correction must 
be added. It is not at all unusual to find manometers used for vacuum 
gages to be comparatively small in diameter, and unless the graduations 
of the scale have been corrected for the error due to capillarity the proper 



POWER PLANT TESTING 



allowances must be made for all observations. Fig. 6 shows by a curve 
the values of this correction as determined by Pullen for mercury columns 
of various diameters. 

Mercury columns should be read at the top of the meniscus and water 
columns should be read at the bottom. In this way, except in very 
small tubes, the errors due to capillarity may be regarded as negligible. 
If the graduated scale is made to lap over nearly half the width of the 
tube on each side, as illustrated in Fig. 2, and all the observations are taken 
at the meniscus in the middle of the tube, a remarkable degree of accu- 
racy is obtainable. 

Mercury barometers are instruments designed to accurately measure 
atmospheric pressure. The one shown in Fig. 7 consists of a glass tube, 
closed at the top and enclosed in a metal casing T. 
The open end of the glass tube at the bottom dips 
into a glass cup C well below the level of the mercury 
with which it is partly filled. The glass cup is closed 
at the bottom by a leather bag resting on a movable 
disk. By means of the screw S the level of the mer- 
cury can be raised or lowered until the surface of its 
meniscus just touches the tip of a fixed ivory point. 
Atmospheric pressure acts upon the mercury in the 
cup so that the height of the mercury column in the 
tube is a measure of this pressure. A vernier is gen- 
erally provided alongside the scale to assist in accu- 
rate observations of the height, which is measured to 
the top of the meniscus. For every observation the 
level of the mercury in the cup C must be adjusted 
accurately to the tip of the ivory point. The equip- 
ment of a modern power plant is incomplete without 
a reliable and accurate barometer. 

Standard barometric pressure for comparison is usu- 
ally taken as 30 inches of mercury at a temperature 
of 32 degrees Fahrenheit. To correct a barometric 
reading and obtain the equivalent height at 32 de- 
grees corrections must be made for both the cubical 
expansion of mercury (coefficient = .000100) and for 
the linear expansion of the scale (coefficient of brass 
= .000011). If H is the barometric reading in inches 
at t degrees Fahrenheit, then the equivalent height 
corrected for temperature (H ) is 




Fig. 7. — Mercury 
Barometer. 



H = H 



(.000100 — .000011) (t — 32) ) 
1 + .000100 (t — 32) ) 



• (1) 



MEASUREMENT OF PRESSURE 5 

This equation is equivalent in English units to the standard correction 
adopted by the International Bureau of Weights and Measures. 1 

Some observers, however, have adopted 62 degrees Fahrenheit instead 
of 32 as the standard for the brass scale, making the correction consider- 
ably more complicated. Whether the scale is corrected to 32 or 62 de- 
grees actually changes the results very little. 

Vacuum measured with a mercury manometer must be corrected to 
standard temperature conditions in the same way as barometer readings 
are corrected. Frequently wooden scales are used on vacuum manom- 
eters. If the scale has been cut so that the length is along the grain 
the expansion is very small (see Table II in the Appendix) and the equa- 
tion above can be simplified for most practical purposes to 

Ho = H - .oooi (t - 32) (1') 

when 32 degrees Fahrenheit is the standard for comparison. 

It often happens that there are tens and even hundreds of feet difference 
in elevation between the location of the barometer and that of the vacuum 
gages. It then becomes necessary to correct the reading of the vacuum 
gages to the elevation of the barometer. The correction is about 0.11 
inch 2 per 100 feet, which is to be added to the vacuum reading when the 
vacuum gage is elevated above the barometer, and vice versa. This cor- 
rection for elevation is often serviceable for determining the approxi- 
mate barometer reading at a place where no barometer is available, by 
applying the corrections to the barometer observation at the nearest 
station of the U. S. Weather Bureau. Observations reported by the 
Weather Bureau are at sea-level and 32 degrees Fahrenheit. To use 
these data it is therefore necessary to know the elevation above sea-level 
of the place where the test is being made, and all observations made with 
mercury columns must be reduced to the equivalent at 32 degrees Fahren- 
heit to obtain correct absolute pressures. (See Report of Power Test 
Committee of American Society of Mechanical Engineers in Journal of 
the American Society of Mechanical Engineers, Nov., 1912, page 1696.) 

Obviously, temperature and elevation corrections are avoided when 
the barometer and the vacuum manometer are hung very near each other. 
To correct observations of vacuum to equivalent vacuum compared to 
(or " referred to ") 30 inch barometer, the difference between the cor- 
rected barometer and 30 inches is added to the observed vacuum when 
the barometer is less than 30 inches, and is subtracted when greater than 
30 inches. This is the method most generally used. 

1 Broch, Bulletin of International Bureau of Weights and Measures (1887). 

2 A cubic foot of air at average atmospheric temperatures weighs about .078 pound 
or (.078 X 100) -=- 144 = .0542 pound per square inch for 100 feet of elevation, which 
is equivalent to .0542 -j- 491 or .11 inch mercury per 100 feet. 



6 



POWER PLANT TESTING 




Fig. 8. — Simplest 
Form of Absolute 
Pressure Gage. 



Aneroid Barometer. Atmospheric pressure is sometimes measured 
by a mechanical device called an aneroid. It is simply a delicate pressure 
gage which is more conveniently portable than a 
mercury barometer. On this account aneroids are 
frequently used in power plant testing and for de- 
termining elevations. They must be frequently cal- 
ibrated by comparison with a mercury barometer. 
Most engineers place more reliance on aneroids than 
their accuracy permits. 

Absolute Pressure Gages. Simplest forms of in- 
struments for indicating directly absolute pressure 
consist of a mercury ba- 
rometer and a vacuum 
gage placed side by side, 
with a sliding scale be- 
tween them, as illustrated 
in Fig. 8. When the zero 
is adjusted so as to be 
exactly opposite the top of the mercury col- 
umn in the barometer, the reading on the 
scale opposite the level in the vacuum gage is 
the absolute pressure. Obviously the scale 
can be graduated to indicate inches of mer- 
cury, pounds per square inch, or any similar 
units of absolute pressure. A simpler com- 
mercial form of absolute pressure gage is 
shown in Fig. 9, designed to show directly 
without adjustment the absolute pressure. 
Essentially it is a barometer with only a very ] 

short tube provided for the mercury column. 
Instead, however, of having the mercury cup 
or reservoir at the bottom open to atmos- 
pheric pressure as in the ordinary barometer, connect! 
the cup C, in this case, is sealed except for condenser 
the pipe P, which is to be connected to the 
chamber in which the absolute pressure is to 
be measured. Before filling the instrument FlG . 9. - Commercial Form of 
with mercury, the tube is exhausted to a prac- Absolute Pressure Gage, 
tically perfect vacuum as for a regular-size 

barometer column. When the pipe P is open to atmospheric pressure, 
the mercury column will be forced all the way to the top of the capillary 
tube; but when this pipe is connected to a vacuum chamber, the mer- 
cury column will gradually fall. If the instrument is well made it should 




MEASUREMENT OF PRESSURE 7 

be fairly accurate for the range between four pounds and one-half pound 
per square inch absolute pressure. Graduations on the left side are 
inches of mercury and on the right, pounds per square inch, absolute 
pressure. ; 

Conversion of Pressures. It is frequently necessary to reduce pres- 
sures in inches of mercury or of water to the equivalent in pounds per 
square inch. Since the weight of a cubic inch of mercury at 70 degrees 
Fahrenheit is .4906 pound and of water at the same temperature is .0360 
pound, pressures in inches of mercury at the usual " room" temperatures 
can be reduced to pounds per square inch by multiplying by .491 or by 
dividing by 2.035, and similarly inches of water can be converted to 
pounds per square inch by multiplying by .0360 or by dividing by 27.78. 
Centimeters of mercury are reduced to pounds per square inch by multi- 
plying by .1903. 

Kilograms per square centimeter are reduced to pounds per square 
inch by multiplying the kilograms per square centimeter by 14.223 or 
by dividing by .0703. Grams divided by 28.35 are ounces 'avoirdupois; 
or one gram is approximately 3 V ounce. 

General metric conversion tables are given in Table III in the Appendix. 

A cubic foot of water at 70 degrees Fahrenheit weighs 62.3 pounds and 
at 30 degrees Fahrenheit, 62.4 pounds. At ordinary " room " temperature 
the pressure due to 2.31 feet of water is equivalent to one pound per 
square inch. 1 

Tubes used as mercury manometers must be cleaned from time to time 
by washing the inside surface with nitric acid and afterward thoroughly 
cleansing them with water. Mercury used in manometers should be free 
from impurities. Usual impurities can generally be removed by filter- 
ing through a clean cloth of close texture or a very thin chamois leather. 
Air can be removed by boiling, but by far the best method for cleaning 
mercury is by means of a mercury still. Unfortunately an apparatus of 
this kind is not available in most engineering laboratories. 

Pressure Gages. The large size necessary, however, for manometers 
or U-tubes, even if filled with the heaviest liquids, makes their use un- 
suitable except for comparatively low pressures. Instruments more 
desirable for high pressures are made by the application of some kind of 
elastic material designed to produce a uniform deformation for variations 
of pressure. By connecting a suitable auxiliary mechanism to the elastic 
element it can be made to move a needle to indicate on a graduated dial 
the degree of pressure. The most common form of such devices is a 

1 The unit pressure of one pound per square inch is equivalent also to that due to a 
column of air of uniform density, of which the vertical height in feet is approximately 
144.0 divided by the weight of a cubic foot of air at the temperature, pressure and 
humidity as observed. Tables of the weight of air are given on page 181. 



POWER PLANT TESTING 



hollow brass or steel tube bent into the shape of an arc of a circle. It is a 

well-known principle that when a straight piece of tubing is bent into 

this shape the sides come nearer 
together, making the section of 
the tube a very much flattened 
oval. 1 A tube of this kind is. 
illustrated in Fig. 10, showing 
also in the right-hand corner a 
transverse section. If one end 
of such a tube is closed and 
fluid pressure is applied to the 
inside, the parallel sides, as at 
A and B, tend to separate and 
consequently there is a ten- 
dency for the radius of curva- 
ture of the tube to become 
larger, thus moving the end at 
E toward F. By connecting a 
suitable mechanism to E, the 
degree of pressure can be in- 
dicated. Instruments of this 
kind are called Bourdon gages. 
Fig. ii shows one of the simplest forms of such gages used in power 

plants to indicate the pres- 
sures. It consists essentially 

of the curved tube T of oval 

cross-section closed at one 

end. This end is connected 

by means of suitable levers 

to a rack R, engaging with a 

small pinion N on the same 

shaft with the pointer or 

needle P. Pressure applied to 

the tube T causes the rack 

and pinion to move over a 

dial (Fig. 12) graduated or 

marked to indicate pressures 

in standard units as, for ex- 
ample, pounds per square inch 

(English system) or kilograms Fig. 11. 




Fig. 10. — A Typical Bourdon Tube. 




Mechanism of Bourdon Tube 



1 For a theoretical discussion of this principle in detail see Theorie der Rohrenfeder 
Manometern in Zeitschrift des Vereines deutscher Ingenieure, Oct. 29, 1910, pages 1865-73. 



MEASUREMENT OF PRESSURE 



9 



per square centimeter (Metric system). Gages are usually most sensitive 
and accurate from about one-half to two-thirds of the maximum gradua- 
tion. The gage shown in Fig. 12 is most suitable for use between 130 and 
175 pounds per square inch. 

Fig. 13 shows a form of Bourdon gage in which the amount of vibration 
of the needle due to the jarring that occurs in locomotive and other port- 




Fig. 12. — The Dial of a Pressure Gage. Fig. 13. — A Modified Bourdon Gage. 



able services has been reduced to a minimum by supporting the pressure 
tube in the middle instead of at its end as in Fig. 11. This form of tube 
has also advantages for use in gages exposed to temperatures below 
freezing, since the arms can be 
drained of water, while the 
other form will usually hold the 
water that has entered. 

In Bourdon gages any lost 
motion of the parts is taken up 
by the hair spring attached to 
the spindle carrying the pointer. 
But the use of a Bourdon pres- 
sure gage under conditions of 
constant vibration due to either 
moving over roads and fields on 
a tractor or to the fluctuation 
of pressure in a pipe due to the 
sharp cut-off of an engine will 
rapidly wear off the teeth of the 
rack R and of the pinion N 
(Fig. 11), so that it is not unusual to find some gages very inaccurate in 
the portion of the scale most used. 




Fig. 14. Fig. 15 

Examples of "Goose-neck" Steam Siphons. 



10 



POWER PLANT TESTING 



Standard 

%" Thread 

for Gage 



Gages to be used to determine the pressure of ammonia have the oval 
tube made of steel instead of brass because the latter material deterio- 
rates rapidly in the presence of ammonia. 

Bourdon gages may be used for indicating the pressures of either liquids, 
steam or gases without observing special precautions if the temperature 

is never much over 150 degrees 
Fahrenheit. If, however, the 
elastic tube in the gage is heated 
above this limit it is likely to 
lose some of its temper. When 
used for steam pressure, there- 
fore, some form of siphon or 
water-seal must always be used 
to prevent steam from entering 
the gage. The forms of siphon 
shown in Figs. 14 and 15 are 
preferred for accurate measure- 
ments, but the types used most 
commonly are illustrated in Figs. 
16-18. Ordinarily brass pipe is 
preferred to iron, because of its better conductivity. This suggestion is 
particularly important for superheated steam. In the siphons shown in 
Figs. 16 and 17 there is always a possibility, however, 
that air carried in the steam may be entrapped at A 
where it forms a cushion, preventing the gage from indi- 
cating the true variation in pressure. Fig. 18 represents 
a very common device for putting a water-seal between 
a steam pipe and a gage. Although not considered as 
effective as some of the other types shown, it has the ad- 
vantage of being more compact. 

Adjustments. The ratio of motion of the pointer with 
respect to that of the tube can be adjusted in most 
Bourdon gages by sliding a set-screw in a slot in the 

short arm of the rack-lever. In the gage illustrated in FlG - 18 - Simple 

Water-seal Steam 





Fig. 16. Fig. 17. 

Examples of Ring Steam Siphons. 




Fig. 11 when the short arm of the rack-lever is made 



Siphc 



longer by adjusting the set-screw, the movement of the 
rack and also of the pointer is reduced for a given deflection of the tube. 
Sometimes when used carelessly, especially when subjected to pressures 
beyond the scale on the dial, the tube of the gage takes a permanent 
" set "; or, in other words, it does not spring back to its original position, 
and the pointer does not come back to the zero mark. In such exigencies 
and also for adjustment after calibration the needle can be forced off 
from its spindle — preferably by the use of a clamp or " needle-jack " 



MEASUREMENT OF PRESSURE 



11 



made by gage manufacturers specially for this service — and then set 
again in position where it should be. 

Another kind of gage in which there is a metallic disk or diaphragm 
instead of a bent tube for actuating the indicating device is sometimes 
used. One of this type is well illustrated in Fig. 19. It consists of a 
corrugated diaphragm clamped around its edge by the flanges of an encir- 
cling chamber. Pressure ap- 
plied on the lower side of the 
diaphragm deflects it upward, 
the amount of this upward 
movement being proportional 
to the pressure. By means of 
a connecting strut S the move- 
ment of the diaphragm is 
communicated to a rack R 
connected to a small pinion 
attached to the spindle of the 
needle indicating the pressure 
on the graduated dial. 

Since the deflection of the 
center of the diaphragm is 
proportional to the pressure 
and is inversely proportional to 
the cube of its thickness, a very 
slight alteration in the thick- 
ness of the diaphragm will 
cause a considerable change 
in the reading of the gage. 

Hydrostatic pressure must be taken into account in some places, 
particularly when a Bourdon or diaphragm gage is used for determining 
the pressure in a boiler or in a water pipe. For example if the gage is 
located below the surface of the water in a boiler the gage will read too 
high, the error being the pressure equivalent to the head of water be- 
tween the surface in the boiler and the center of the gage. The correc- 
tion in pounds per square inch is .433 times the head in feet. To make 
this correction unnecessary the gage, if of the Bourdon type, should be 
located so that its center will be at about the average water-level in the 
boiler; and if it is of the diaphragm type, the diaphragm should be at 
about the average water-level. 

The practice of choking the gage cock to reduce vibrations of the 
pointer, unless done very carefully, is objectionable, especially when there 
is leakage around the joint of the plug in its cock. Under these circum- 
stances the true pressure will be greater than that indicated. 




Fig. 19. — A Typical Diaphragm Gage. 



12 POWER PLANT TESTING 

Tapping a gage, preferably on the back, just enough to observably 
move the pointer, is an essential precaution to take before reading a 
gage having levers, racks, and springs in its mechanism. This pre- 
caution is necessary to be certain that all working parts are moving 
freely. (See Report of Power Test Committee in Journal of A.S.M.E., 
Nov., 1912, pages 1695-6.) 

Vacuum Gages. For the measurement of vacuum instead of pressure 
Bourdon gages are very commonly used. The design for a pressure 
gage is altered only in the arrangement of the levers moving the needle, 
which for vacuum measurements turn the needle in the same direction 
as for pressure (clockwise); but in this case, the tube is bent inward 
or toward the center of the gage instead of outward as for pressure 
measurements. Vacuum gages are usually graduated to read inches of 
mercury below atmospheric pressure. Absolute pressure in inches of 
mercury is the difference between the barometer and the reading of such 
vacuum gages. 

A vacuum gage is generally used to determine the tightness of vacuum 
lines, condensers, etc. If the line is tight the gage will show no appre- 
ciable diminution of vacuum for several hours, but it drops quickly if 
there are leaks. These are most readily located by bringing a candle 
flame close to all the possible places of leakage. The flame will be drawn 
strongly toward the leaks by the current of air which is being drawn into 
the pipe by the vacuum inside. 

Another type known as a compound gage is used to indicate either 
pressure or vacuum on the same dial. The linkages are adjusted differ- 
ently from those in the usual types in that the position of the pointer for 
zero gage pressure would now be at about the point marked 140 in Fig. 
12. Graduations to the left around the dial would be from zero to thirty 
inches of mercury (vacuum), and similarly, to the right, from zero to 
about fifteen pounds per square inch. Such a device permits using a 
gage with a single Bourdon tube for measuring either vacuum or a con- 
siderable range of pressure. 

Differential Gages are designed to read directly pressure difference. 
Most commonly they are U-tube manometers or equivalent devices 
arranged to have each side (or leg) connected to a source of pressure. 
The displacement of the liquid columns of the manometer will indicate 
the difference in pressure. In Fig. 226 (page 182) the U-tubes marked 
a are good examples of differential manometers or gages. Such gages 
are very satisfactory for such purposes as measuring the difference in 
pressure on the two sides of an orifice in steam, air, or water pipes. 

Recording Gages. In many modern power plants recording gages are 
used to give a graphic record on a chart of the pressure or vacuum for 24 
hours. The most common type of recording gage is shown in Fig. 20. 



MEASUREMENT OF PRESSURE 



13 





14 



POWER PLANT TESTING 





MEASUREMENT OF PRESSURE 



15 




Fig. 24. 



These gages are made usually in one of the three following forms: (1) a 
circular tube of oval section in the form of a helix, as illustrated in 
Fig. 21, (2) with a metallic Bourdon tube, as shown in Fig. 22, or (3) 
with a diaphragm device, as 
in Fig. 23. In the instru- 
ment shown in Fig. 23 the 
diaphragms spread out like 
an accordion when subjected 
to pressure on the inside. 
The first and second of these 
three types are generally used 
for cases where the maximum 
pressure is greater than three 
pounds and the third when it 
is less. The recording arm is 
preferably attached directly to 
the moving element so that 
no gears, levers, or other mul- 
tiplying devices are needed. 
A more compact and less ex- 
pensive form of such gages is 
illustrated in Fig. 24. 

The average pressure cor- 
responding to an irregular curve traced on the circular card of one of 
these recording gages is obtained with a fair degree of accuracy by in- 
tegrating the curve by means of a Durand-Bristol integrating instrument 
described on page 87. Corrections to be applied to the readings of these 
gages are of course obtained by calibrating in the same way as for an 
indicating gage. 

Still another type of recording pressure gage of the Bourdon tube 
pattern is shown in Fig. 25. 

Calibration of Gages. Until recent years when the so-called " dead- 
weight " apparatus for testing gages came into general use, gages used 
in other places than engineering laboratories were commonly calibrated 
by comparison with a so-called test gage. Such test gages have usually 
somewhat finer graduations than the ordinary gages used in practice 
and are probably also adjusted a little more accurately. They should 
never be exposed to the severe conditions of service, being intended 
only for purposes of comparison. This comparison of pressure gages 1 
can be made anywhere by connecting the standard and the gage to be 
tested to any system of piping in which the pressure can be varied either 

1 Calibration of vacuum and low-pressure gages is discussed in another section, 
see pages 22. 



A Very Compact Type of Recording 
Gage. (Bristol.) 



16 



POWER PLANT TESTING 




Fig. 25. — A Combined Recording and Indicating Pressure Gage. 



by pumping a liquid or by means of valves " throttling " steam, water 

or air under pressure. 
The only important pre- 
caution to observe is that 
the two gages shall be at 
approximately the same 
level when a liquid is used, 
and that the velocity of 
the fluid in the main pipe 
to which the gages are at- 
tached is negligible or is 
the same at the points 
where the connections for 
the gages are inserted in 
the " main " pipe. Test 
gages must, of course, be 
calibrated from time to 
time with some standard 
A bench pump suitable for cali- 




Fig. 26. — A Bench Test Pump. 



apparatus to insure their accuracy 

brating by comparison is illustrated in Fig. 26. 



MEASUREMENT OF PRESSURE 



17 



Gage Testers. In very many power plants the use of the test gage 
has been superseded by some form of gage tester and by this means the 
gages used in the plant can be calibrated directly with an absolute 
standard. Calibrations of gages for high pressures by means of mercury 
columns are for practical reasons suitable only for laboratory work. 

Dead-weight Gage Testers. The best-known form of this apparatus 
is made by the Crosby Steam Gage and Valve Co., and is illustrated in 
Figs. 27 and 28. The latter 
figure shows a partial section. 
It consists of a vertical cylin- 
der C, into which is fitted 
very accurately a plunger P, 
of which the area, when new, 
is exactly one-fifth of a square 
inch. A circular platform upon 
which weights can be placed is 
attached to the upper end of 
this plunger. The cylinder C 
communicates at its lower end 
with the reservoir R fitted with 
an adjustable piston working 
in a screw and is operated by 
a hand wheel. A pipe T at- 
tached to the lower part of 
the reservoir is provided with 

unions and special fittings for attaching gages of various sizes. In the 
horizontal portion of this pipe there is a three-way cock or valve V for 
either draining the reservoir or for closing the pipe so that the liquid in 

the apparatus will not escape 
when the gage is removed. 
In operation, after the gage 
has been attached securely, 
the piston is screwed down 
to the bottom of the reservoir 
R, then with the plunger P 
removed, glycerine or heavy 
oil is poured into the cylinder 
C at the same time that the 
piston is screwed out. In this 
way the reservoir can be com- 
pletely filled with oil without 
entrapping any considerable amount of air which would act as a cushion 
preventing the most satisfactory operation of the apparatus. 




Fig. 27. — Crosby Dead-weight Gage Tester. 




Fig. 28. — Section of a Dead-weight Gage Tester. 



18 



POWER PLANT TESTING 



If the area of the plunger P is one-fifth of a square inch then each 
pound weight added on the platform produces a pressure on the liquid 
of 5 pounds per square inch. The weight of the platform and plunger 
(usually 1 pound) must always be included in the weight producing 
the pressure. As the load on the platform is increased the piston must, 
from time to time, be screwed in to keep the platform " floating." When 
observations are being taken it is very essential that the loaded platform 
be given, preferably by hand, a slight rotary motion to reduce to a mini- 
mum the friction of the plunger in its cylinder. 

Suggested Procedure with Dead-weight Testers. The accuracy of 
the gage to be calibrated is determined by subjecting it to known pres- 
sures and noting its error. 
Before the plunger P has 
been put into place the 
reading of the gage, called 
" zero-reading," should be 
observed and recorded in a 
form similar to the one on 
page 21. Then the pres- 
sure should be increased 5 
pounds per square inch at 
a time (corresponding usu- 
ally to a weight of 1 
pound) up to the limit of 
the graduations on the 
dial, spinning the piston 
gently when each reading 
is taken. Commencing 
then with the highest pres- 
sure the same operation 
should be repeated by de- 
creasing the pressure by 
the same increments. 1 
In case there is an ap- 
preciable difference between the area of the plunger P and its cylinder C, 
the two areas should be averaged to obtain the true area to be used in 

1 When the pressure is being • decreased the movement of the pointer must be al- 
ways in a counter-clockwise direction just before a reading is taken. In other words, 
if a weight of 2 pounds has been taken from the load on the plunger when only 1 pound 
should have been removed, the pointer will, of course, get below the next point to be 
calibrated. To secure the reading missed it will not be correct to add I pound and 
take the reading, because the friction and lost motion will now be in the same direction 
as with increasing pressures; and to overcome this difficulty the pressure must be in- 
creased again to a value higher than that for which the reading is to be taken. For 




Fig. 29. — Crosby Portable Fluid Pressure Scales. 



MEASUREMENT OF PRESSURE 



19 



calculating the unit pressure. In other words, the true pressure exerted 
on the fluid in the apparatus in pounds per square inch is the total weight 
in pounds divided by this average area in square inches. (Report of 
Power Test Committee of A.S.M.E., 
Nov., 1912, page 1695.) 

A modification of the dead-weight 
gage tester is shown in Fig. 29. This 
instrument is particularly suited for 
calibrations at high pressures. Its 
range is from to 1500 pounds per 
square inch. Any pressure within 
these limits can be obtained without 
shifting heavy weights. Readings 
are taken when the scale beam is 
balanced. The hand wheel A is used 
to regulate the fluid pressure by 
means of a piston as in the appara- 
tus shown in Figs. 27 and 28. The 
other hand-wheel B shown in the 
figure must be kept rotating when 
observations are taken. The slight 
jarring of the parts due to its rota- 
tion serves to make the friction as 
small as possible. Particularly in 
the case of gages that have had severe usage so as to be badly worn, it is 
necessary to tap the back of the casing of the gage lightly before each 
reading is taken to be certain that the pointer is moving freely. 

For still higher pressures up to 12,000 pounds per square inch, a heavy 
stationary type, shown in Fig. 30, can be used. 

Calibration of Gages with Mercury Columns. The ultimate standard 
for the determination of reasonably high pressures is the mercury column, 
but the apparatus required is so complicated and occupies so much space 
that this method is suitable only for use in laboratories where it will have 
the attention of skilled observers. 

For the purpose of calibrating steam gages mercury columns have been 
fitted up in a variety of ways. The simplest of these is the method of con- 
necting the gage to be tested by means of a short tube to a " closed " 

the purpose of increasing the weight it is not necessary to put on more weights, as 
additional load in such cases can be put on by the pressure of the hand. 

The same precautions apply with even greater force to calibrations made with 
test gages or with a mercury column. With either of these instruments discrepancies 
may occur with increasing or decreasing pressures. In fact the only certain way to 
get satisfactory results with these instruments is to keep the pointer of the gage or 
the mercury column, as the case may be, moving continually in the same direction. 




- Fluid Pressure Scales for 
High Pressures. 



20 



POWER PLANT TESTING 



mercury well into the top of which a long glass tube has been inserted. 
The pressure can then be increased either by displacing some of the mer- 
cury in the well by means of the plunger in the mercury pump, shown at 
the right-hand side of Fig. 31, and forcing 
it up into the glass tube, or else by pour- 
ing mercury into the tube from the top as 
must be done in the apparatus shown, in 
Fig. 32. Zero pressure for comparison is 
to be taken on the column at the same 
level as the center of the gage. Beginning 
then with 5 pounds per square inch pres- 
sure on the gage observe the corresponding 





Standard Mercury Column and 
Hand Pump. 



Fig. 32. — Simple Open 
Mercury Column. 



height of the mercury column and its temperature, and then continue 
the observations, first increasing the pressure and then decreasing by 
increments of 5 pounds, as indicated by the gage. Equivalent units for 
calibration can be computed from the height of the mercury column, 



MEASUREMENT OF PRESSURE 



21 



since 1 inch of mercury at 70 degrees Fahrenheit is equivalent to a pres- 
sure of .4906 pound per square inch. 

When using a mercury-testing apparatus it is necessary to observe the 
temperature near the mercury column in the room in which the work is 
being done, so that the observed height of the mercury column can be 
corrected to a temperature at which the relation between pressure in 
pounds per square inch and height is known. The coefficient of cubical 
expansion of mercury is not constant, as will be observed from the fol- 
lowing table: 

Temp. Deg. Coefficient of 

Fahr. Cubical Expansion. 

32 0000998 

50 0001000 

70 0001002 

90 0001004 

110 0001007 

For very accurate work allowance must be made for the linear expan- 
sion of the graduated scale. Coefficients of expansion of metals are 
given in the Appendix, Table II. 

Instead of connecting the gage directly to the mercury well, it is some- 
times connected to one end of a steam drum and the mercury column is 
connected to the other. The increments of pressure are then obtained 
by increasing or decreasing the steam pressure in the drum. 

Observations taken in the calibration of a steam gage should be re- 
corded and the computed errors tabulated in a form similar to the fol- 
lowing: 

CALIBRATION OF PRESSURE GAGE. COMPARISON WITH GAGE TESTER 

Date Observers 

Maker of gage Maker's No 

Laboratory No Limits of Graduation 







Gage Readings. Lbs. per sq. in. 


Actual 


Mean Error 




No. of 


Weight on 




Pressure. 


of Gage. 




Reading. 


Tester. Lbs. 








Lbs. per 


Lbs. per 


Remarks. 






Up. 


Down. 


Mean. 


sq. in. 


sq. in.i 





















1 When the sign is +, the correction ("error") should be added, and when 
be subtracted from the observed reading. 



-, should 



22 



POWER PLANT TESTING 



The error of the gage is determined by the comparison of the mean of 
the up and down readings with the actual pressure. 

Curves. From the data tabulated two curves are usually plotted: 

1. Mean gage readings (abscissas) and actual pressures (ordinates). 
Use a large sheet of coordinate paper for this curve. Unless plotted to a 
very large scale, however, such a curve will be of little value. 

2. Error Curve: Mean gage readings (abscissas) and mean correc- 
tions, positive and negative (ordinates). See curve in Fig. 33. Error 
curves should have the points, if very irregular, connected by a broken 
line rather than by a " fair " or average curve through them. Never, 
however, try to draw an irregular curve through each of a number of 
scattered points when the points are supposed to follow a definite relation 



4-4 


-H-( 1 ] !_ t ! i-- f i ' |" ! -:1 M '" j ! ^ti-i ! ! H ■ l i 1 : i J - ! l l i- ' ' i ! : ' ' 1 ' ' ; ! 1 ' ' 1 '■ 






a 


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fi lifmH 


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ffffi If: 




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1 1 1 1 1 1 iii ii n i it 1 1 1 









10 20 



40 50 60 70 ^80 90 100 110 120 130 140 150 
Mean Gage Readings. Lbs. per Set. In. 



Fig. 33. — Typical Error Curve for a Pressure Gage. 

or law between the coordinates selected. A " fair " curve should then 
be drawn between the irregular points. 

Calibration of Vacuum and Low-pressure Gages. A vacuum gage is 
usually calibrated by connecting it to one end of a U-shaped glass tube 
of which both legs are about 30 inches long and are filled to about half 
their length with mercury. The U-tube and gage are then connected 
to the receiver of an air-pump or else to an aspirator or ejector operated 
by water or steam pressure, such as chemists use for vacuum filtering. 
The aspirator (Figs. 276 and 277, page 236) is really the more convenient 
instrument to use. If the readings of the vacuum gage are correct, they 
will correspond exactly with the difference in the level of the mercury in 
the two legs of the U-tube. 

In case a condensing engine is operating when the calibration of the 
vacuum gage is to be made, both the gage and the glass U-tube may be 



MEASUREMENT OF PRESSURE 



23 



connected to the condenser. A comparison of the readings taken will 
show, under the best possible conditions, the absolute errors of the gage. 
A suitable scale about 30 inches long and accurately graduated should, of 
course, be provided and placed between the two legs of the U-tube. 

An apparatus consisting of an air-pump designed for a high vacuum 
and a mercury column is illustrated in Fig. 34. It is a very convenient 
means for testing vacuum gages. 1 




Fig. 34. — Air Pump and Mercury Columns for Testing Vacuum Gages. 

A low-pressure gage with a scale from say to 15 pounds per square 
inch is very easily and accurately calibrated by using the same glass U- 
tube mentioned for the calibration of the vacuum gage with air pressure, 

1 When measuring inches of vacuum by means of a single mercury column dipping 
into a cup, the zero is to be taken at the level of the mercury in the well into which 
the glass vacuum tube enters. The elevation of the gage above the surface of the 
mercury in the well is not to be considered, as the weight of the column of air 
between the center of the gage and the level of the mercury is negligible. Regarding 
the use of vacuum gages on water suction pipes see sections on Hydraulic Machinery. 



24 



POWER PLANT TESTING 



preferably, or with steam pressure. Otherwise the method for calibra- 
tion is the same as for a vacuum gage, except that inches of pressure 
instead of inches of vacuum are observed. 

Draft Gages. Many engineers use an ordinary glass U-tube manom- 
eter (Fig. 35) filled with water for measuring small pressures like that 
due to the draft in a chimney or that produced in air- 
ducts by ventilating fans or blowers. For such ob- 
servations in many cases, however, greater accuracy 
is desired than can be secured by the use of the ordi- 
nary U-tube and a special form of manometer is used 
in which the distance moved by the surface of the 
liquid in the tube is greater than the vertical change 
of level. Fig. 36 illustrates a simple device of this 
kind. It consists of a bottle B, filled with water, 
having a suitable opening at the bottom to which by 
means of a short rubber tube the inclined glass tube 
CD is attached. At the upper end of this tube a 
piece of rubber tubing T is shown and is intended to 
be connected to the chimney, duct, or flue in which 
the pressure is to be obtained. A scale placed behind 
the inclined tube CD should be graduated so that 
when the spirit level L is adjusted, vertical differences 
in level of the liquid in CD will be indicated by its 
graduations. Then differences in the readings of the 
scale will give directly the difference in pressure in 
inches of water just as with an ordinary U-tube. Un- 
less the bottle B is very large in diameter it is best to 
mark the graduations on the scale for every half inch by comparison 
with a U-tube 1 like Fig. 35. Intermediate divisions can then be marked 
with the help of dividers. 




Fig. 35. — Simple 
U-tube Draft Gage 




Fig. 36. — Inclined Tube Draft Gage. 

1 This method for graduating and also for checking the graduations is recommended 
by the Power Test Committee of A.S.M.E. For this special service the use of alcohol 
is advised instead of water in the U-tube, but allowance must be made for the differ- 
ence in specific gravity between water and alcohol. It would be impracticable to use 
alcohol in gages that are in continuous service as the ordinary draft gage must be open 
to the air at one end, and the alcohol would very rapidly vaporize. 



MEASUREMENT OF PRESSURE 



25 



Very accurate draft gages of this type, known as Ellison's, are shown in 
Figs. 37 and 38. The inclination of the tube in these instruments is 
usually about 1 to 10. Instead of water a very light oil is used to fill the 
tube. It is claimed that this oil has the advantages of having less capil- 
larity than water, and also, being lighter, permits the use of a longer scale 




Fig. 37. — Ellison's Improved Draft Gage. 

for a given difference in level. Graduations on these instruments which 
are sold commercially 1 are, however, always made to read equivalent 
inches of water. These draft gages are also often used for measuring 
small differences of pressure. For example, if there are two vessels con- 
taining gases at different pressures and one is connected to the left-hand 
side and the other to the right-hand side of the gage, it will indicate the 
difference in pressure. When used in this way it is called a differential 
gage (see page 12). 




Fig. 38. — • Ellison's Differential-direct Draft Gage for High Drafts 



Graduations on all such instruments should be checked by comparison 
with a simple U-tube, filled with distilled water (condensed steam from 
a surface condenser is satisfactory). The U-tube should be provided 
preferably with a steel scale of a recognized standard make. 

When calibrating gages it is worth while to notice that when instru- 
ments are to be used to observe practically constant values it is necessary 
to calibrate them only near the values to be observed. 

1 American Steam Gage and Valve Mfg. Co., Boston and Chicago. 



26 



POWER PLANT TESTING 




Fig. 39. — Simplest 
Two-fluid Type of 
Manometer. 



Draft gages which have liquids of slightly different densities combined 
so as to magnify the difference in level are sometimes used. Generally 
such an instrument consists of a U-tube with the top ends of very large 
area 1 and the connecting portion of small capillary 
tubing. Obviously the liquids used must have very 
little tendency to mix together or to become diffused. 
Fig. 39 shows one type of such gages. As illustrated 
the U-tube was first partly filled with the heavier 
liquid, and afterward a lighter liquid was poured into 
each leg so as to completely fill the capillary and also 
fill partly each of the vessels A and B. The level of 
the separating meniscus on either side can be used as 
the indicator. Since the area of the capillary is very 
small compared with that of the vessels A and B, the 
indicating meniscus receives quite a large displace- 
ment for small differences in pressure. If the liquids 
used are kerosene (sp. grav. = .80) and brandy (sp. 
grav. = .94) the displacement of the separating meniscus due to pres- 
sure or vacuum will be about seven times the equivalent inches of water. 
Instruments of this type are usually graduated 
to indicate the pressure in inches of water. 

A very delicate draft gage can be made also 
by using the apparatus of Fig. 39 in a little 
different way, as in Fig. 40. Water is put into 
A and oil into B, with the surface of separa- 
tion originally at Q, when A and B are both 
subjected to the same pressure. When B is 
connected to a chamber in which there is a 
vacuum as in the breeching or the chimney of 
a power plant the levels are changed from F 
to E in B and from C to D in A. The surface 
of separation moves from Q to R. Let CD = 
EF = x inches, QR = y inches, and s = specific 
gravity of the oil, then the change of pressure p in inches of water] in A 
and B is 

p = x + sx + y (1 - s). 

If the areas of A and B are equal and are n times the area of the connect- 
ing tube, then y = nx, and p = + y (1 — s) = y h 1 — s . 

Observe that'the smaller the factor in the brackets the greater will be the 
magnification or sensitiveness. The value of n should therefore be made 



/? Connection to 
Vacuum Chamber 



l: 



Fig. 40. — Another Type of 
Two-fluid Manometer. 



Preferably these top ends should be made with constant sectional area. 



MEASUREMENT OF PRESSURE 27 

as large as possible, say about 100, and the two liquids should be pref- 
erably of nearly the same specific gravity. Gasoline and brandy are 
frequently used for the two liquids. They are of nearly the same specific 
gravity and the line of separation is readily observable. If S is the 
specific gravity of the brandy and s that of the gasoline, obviously 

, v p±± + s-4 

Values of pressure causing a given movement of the line of separation 
may be calculated from the equations above, but actual calibration by 
comparison with an ordinary U-tube and graduation by exterpolation 
as recommended by the American Society of Mechanical Engineers is 
always preferable. 

These last types of draft gages are too delicate for ordinary service in 
power plants to measure draft, but are particularly well suited for use with 
Pitot tubes in measuring air velocities as discussed in Chapter VII. 



CHAPTER II 

MEASUREMENT OF TEMPERATURE 

Mercurial Thermometers. Temperatures less than about 500 degrees 
Fahrenheit are usually measured by means of mercurial thermometers, 
depending for their action on the expansion of mercury in a glass bulb 
and a graduated capillary tube. 1 The ordinary type is made so as to 
have merely a vacuum in the capillary tube above the mercury. For 
use at higher temperatures the capillary may be filled with nitrogen gas 
when the thermometer is made. It will then be serviceable up to 1000 
degrees Fahrenheit. Thermometers made of quartz instead of glass and 
filled with nitrogen or carbonic acid gas can be used for temperatures 
as high as 1500 degrees Fahrenheit. Quartz thermometers are much 
stronger than those made of glass but are too expensive for ordinary 
commercial use. 

Whenever mercurial thermometers are used for any work where reason- 
able accuracy is expected they should be carefully calibrated before the 
test is made; and after the test the calibration should be at least roughly 
checked to be sure that the zero of the thermometer has not changed. 
Too often it happens in practice when tests are being made, as for ex- 
ample of a boiler or of a steam turbine, that in some way a thermometer 
not previously calibrated has been used, and before the end of the test 
is broken. It is then too late to get a calibration and sometimes very 
important results of tests are made doubtful because of such negligence. 
The " Instructions Regarding Tests " of the American Society of Me- 
chanical Engineers require that all thermometers used shall be calibrated 
both before and after every test where important data are to be obtained. 

Calibrations of thermometers of all kinds must be made often because 
there is always the possibility that a little of the mercury has become 
detached from the column and remains unobserved either on the sides 

1 The best thermometers for ordinary engineering work are those having graduations 
etched on the stem and filled with ink. This is the only type of' thermometer recom- 
mended by the Power Test Committee of the A.S.M.E. After considerable use, how- 
ever, the ink originally in the etched markings disappears and it becomes difficult to 
read the scale. When this happens a thick paint made of lampblack and shellac or 
printer's ink can be rubbed over the etched scale, and when this paint is rubbed off, 
after a few minutes, there will be enough of it left in the etchings to make the scale as 
legible as when new. A crayon or pencil of soft greasy graphite like those used by 
glaziers for marking glass or by shippers for marking cases is a satisfactory substitute 
for the paint, although it is not so permanent. 



MEASUREMENT OF TEMPERATURE 29 

or at the top of the capillary tube. In all glass thermometers there is 
always taking place with use and time a gradual and permanent change 
in the volume of the bulb, more in new thermometers than in old ones, 
altering the zero point and, of course, also the true values for all the 
graduations. 

Alcohol Thermometers. For the measurement of temperatures much 
below zero Fahrenheit thermometers filled with mercury are not satis- 
factory, and alcohol or " spirits of wine " is used. These liquids, on the 
other hand, are not suited on account of their high vapor tensions for 
high temperatures. 

Conversion of Temperatures and Heat Units. Temperatures in Centi- 
grade degrees are converted into Fahrenheit by multiplying by f and 
adding 32. Kilogram-calories 1 multiplied by 3.968 give the equivalent 
British thermal units (B.t.u.), and kilogram-calories per kilogram X 1..8 
give British thermal units per pound. A " small " or gram-calorie is 
one-thousandth as large as a kilogram-calorie. 

Calibration of Thermometers. Tests to determine the accuracy of 
thermometers are made by subjecting them to known temperatures and 
noting the errors. This is done usually in one of two ways: 

1. By comparison with a so-called " standard " thermometer known 
to be accurate. 

2. By comparison with temperatures corresponding to steam pressures. 
Since the second method is not applicable for temperatures below the 

boiling point of water, it is not often used below 212 degrees Fahrenheit. 
For " low-reading " thermometers, therefore, the first method is generally 
used. 

" Standard " thermometers for comparison should be preferably those 
which have been calibrated at standardizing laboratories, such as at the 
U. S. Bureau of Standards at Washington, D. C, at the Reichsanstat at 
Berlin, Germany, or at the National Physical Testing Laboratories in 
London, England. The steam laboratories of nearly all technical col- 
leges have sets of standard thermometers suitable for determining the 
errors of good thermometers to be used as " secondary " standards. 

After once calibrating a high-grade " standard " thermometer, it can 
usually be assumed that the calibrations throughout the range of its 
scale have not changed if the " ice-point " reading (for low-scale ther- 
mometers) and the " steam-point " reading at atmospheric pressure (for 
high-scale thermometers) remain unchanged. Checking either the " ice- 
point " or the " steam-point " at frequent intervals is the method ad- 

1 In German literature kilogram-calories are generally called Warme Einheiten, 
usually abbreviated to W. E. For a scientific discussion of the distinction between 
"mean" calorie and "15 degree" calorie see Granberg's Technische Messungern, pages 
250-252. 



30 



POWER PLANT TESTING 



vised by the U. S. Bureau of Standards for determining whether any 
appreciable change has occurred in laboratory standards to make a new 
and complete calibration necessary. 

The " ice-point " reading can be made by immersing the thermometer 
to the graduation marking 32 degrees Fahrenheit in good ice scraped from 
transparent cakes and mixed with the water obtained from its melting. 1 





The Right Way. The Wrong Way. 

Fig. 41. — Typical Thermometer Wells — "Good and Bad." 

Thermometers used at high temperatures should have the " steam- 
point " checked frequently in an apparatus like Fig. 43 (page 33). 

The following paragraphs concerning standard thermometer wells, 
thermometers for high degrees of superheat, etc., are from the Nov., 



See Circular No. 8, Bureau of Standards. 



MEASUREMENT OF TEMPERATURE 31 

1912 Report of the Power Test Committee of the American Society of 
Mechanical Engineers: 

"Standard thermometers are those which indicate 212 deg. Fahr. in steam es- 
caping from boiling water at the normal barometric pressure of 29.92 in. (re- 
ferred to 32 deg.), the whole stem up to the 212 deg. point being surrounded by 
the steam; and which indicate 32 deg. Fahr. in melting ice, the stem being likewise 
completely immersed to the 32 deg. point; and which are calibrated for points 
between and beyond these two reference marks. 1 

"A thermometer well consists of a hollow cup or plug threaded at the upper end 
and screwed into a threaded hole in the top of a horizontal pipe, the lower part 
extending vertically into the interior of the pipe as far, if practicable, as the center. 
The inside diameter should be slightly larger than the outside diameter of the ther- 
mometer tube and the well should be filled with mercury or high-grade mineral 
oil for temperatures below 500 deg. and with soft solder for higher temperatures. 

"For superheated steam the portion of the well exposed to steam should be fluted 
or channeled so as to increase the area of the absorbing surface. 

"Thermometers are so readily broken that it is desirable in important tests to 
have a sufficient number on hand that in case of accident the readings will not be 
interrupted. These spare thermometers should be calibrated in advance." 

Experience has shown that certain types of thermometer wells for use 
in pipes give more satisfactory results than others. The thermometer 
well must be long enough to enter well into the pipe so that the flow of 
fluid through it will be around the well. In other words it should be 
located so that it will be in the " main stream " and not in such a position 
where only eddies touch it. A well-designed thermometer well is illus- 
trated in the left-hand half of Fig. 41. On the right-hand side there 
is a correspondingly very poor design. To be sufficiently sensitive to 
temperature variations the bodies of such wells should be made of brass 
and the thickness of the metal where directly exposed to steam should 
not exceed T V inch. Steel and wrought-iron wells are, however, fre- 
quently used in ordinary commercial power plant work. 

Calibration by Comparison with a Standard Thermometer. For low- 
temperature calibrations the thermometers to be tested are usually 
suspended together with a " standard " thermometer of which the errors 
are known in a water bath arranged so that the temperature can be varied. 
This bath may consist simply of a vessel provided with a coil of pipe 
through which steam can be circulated and has also a suitable stirring 
device. If the water is kept well stirred in such an apparatus a uniform 
temperature can be maintained and three or four thermometers can be 
calibrated at the same time. 

1 This definition of standard thermometers must also include any high-grade ther- 
mometers of which the errors throughout the scale are accurately known. It is prac- 
tically impossible to make thermometers that will be absolutely accurate. 



32 



POWER PLANT TESTING 



Fig. 42 illustrates diagrammatically a very simple apparatus of this 
kind, except that the water bath is heated by discharging steam directly 
into the water. This arrangement permits changing the temperature 
more rapidly than with the coil of pipe mentioned above. 

When the method of comparison with a " standard " thermometer is 
to be used for temperatures higher than are obtainable with this appara- 
tus, the " standard " thermometer and the other thermometers to be 
calibrated are placed in adjacent cups or wells inserted in a suitable cylin- 
drical drum with pipe connections permitting a flow of steam around the 
thermometers. Fig. 43 shows a good design of this apparatus. Steam 




Fig. 42. — Apparatus for Calibration of Thermometers at Temperatures Less than the 
Boiling-point of Water. 



passes through the regulating or needle valve A and enters the large 
cylindrical drum through the pipe C, which is open at the lower end. 
Exhaust is through D. A water gage is provided to show the level of 
water. Obviously if the bottom of the long thermometer well is im- 
mersed in watery the temperature indicated would not be comparable, 
as a rule, with the shorter thermometer exposed entirely to steam. The 
top of the exhaust pipe is made higher than the bottom of C so that there 
will always be some water " trapped " in the cylinder; and the steam 
which enters must bubble up through this water, making it more certain 
that the steam to which the thermometers are exposed is wet. In 
other words, the superheating which is likely to be caused by throt- 



MEASUREMENT OF TEMPERATURE 



33 



tling with the regulating valve A must be eliminated. Although only- 
two thermometers are shown the apparatus can be very conveniently 
fitted with four or six thermometer wells so that a greater number can be 
calibrated at a time. The thermometer cups or wells should be filled 
with cylinder oil or, preferably, for high temperatures, with mercury. 1 
Temperature is varied by throttling with the valves on either or both 
the steam inlet and discharge pipes. Usually the necessary adjust- 
ment is made more easily by manipulating the discharge valve rather 
than the inlet. At least five minutes should be allowed after the valves 




*% Pipe 
Fig. 43. — Apparatus for Calibration of Thermometers with Saturated Steam. 



have been adjusted for the mercury in the thermometers to come to rest 
before readings for comparison are taken. Readings of both the standard 
and the thermometer being calibrated must be taken as nearly as possible 
at the same time, and the thermometers should be lifted from their cups, 
when necessary, just enough to bring the mercury into view. Observa- 
tions should be taken as quickly as possible to avoid errors due to cool- 
ing and should be made with approximately the same increments. 



1 If oil is used in thermometer cups, precautions should be taken that the oil is 
absolutely free from the presence of water and that there is no water in the cups. If 



34 



POWER PLANT TESTING 



The method of calibrating thermometers for temperatures between 
212 and 400 degrees Fahrenheit by comparison with steam tables, as 
explained below, is more generally used than the method above. 

A record of the observations should be made in the following form : 



CALIBRATION OF THERMOMETER 



By comparison with "STANDARD" 

Date Observers 

Standard : Thermometer Tested : 

No. or distinguishing mark No. or distinguishing mark . 

Range of scale Range of scale 





Standard 
Thermometer. 


True Tem- 
perature. 


Thermometer Tested. 




No. 














Reading. 


Known 

Error. 1 




Reading. 


Error.i 

(+or-) 


Remarks. 




°F. 


°F. 


°F. 


°F. 


°F. 



















1 When the sign is +, the correction ("error") should be added, and when — , should 
be subtracted from the observed reading. 

Calibration of Thermometers by Comparison with Temperatures 
Corresponding to Steam Pressures. There is a definite temperature 
of saturated steam corresponding to every pressure. If, then, the 
pressure is known, the temperature corresponding can be obtained from 
" Tables of the Properties of Saturated Steam." 1 

Thermometers to be calibrated are placed in adjacent cups or wells 
of the same depth inserted in a cylindrical steam drum and filled with 
cylinder oil or mercury. Pipe connections must be provided for the 
attachment of an accurately calibrated steam gage, and valves are needed 
at the ends of the drum for regulating the flow of steam through it. The 

water is allowed to accumulate there may be a slight explosion, sometimes strong 
enough to throw the thermometer out of the cup. 

Thermometers used for measuring high temperatures should be protected from con- 
tact with the metal of the cups by wrapping the stems at the mouth of the cup with 
cotton waste or with rings of cork. 

1 Marks and Davis' Steam Table and Diagrams or Peabody's Steam and Entropy 
Tables (revised 1909) are recommended. 



MEASUREMENT OF TEMPERATURE 



35 



apparatus used is the same as that explained for calibration with a 
standard at high temperatures. Fig. 43 shows the apparatus complete 
with a steam gage attached. 

It is very important that the thermometer being calibrated should be 
immersed in the well to the same extent as it will be when in use. It is 
a very good arrangement to have a standard type of well for all ther- 
mometers of the same length, so that if a thermometer has been cali- 
brated in one of these standard wells the calibration will be applicable 
in any one of these wells, provided the " room " temperature does not 
vary widely. Effect of variations of " room " 
temperatures can be readily calculated by the 
method explained on pages 36 to 38. 

Calibration sheets for use with this method are 
made up like the one on page 34, except that 
pressure by the gage 1 is recorded instead of the 
temperature indicated by the " standard " ther- 
mometer. 

If the steam supplied to the cylinder is super- 
heated, then it is necessary to provide a water- 
jacket around the steam pipe large enough to 
make the steam at least dry saturated or prefer- 
ably slightly wet. Another device often used to 
change superheated steam to the saturated con- 
dition is illustrated in Fig. 44. In principle it is 
the same as Fig. 43. In this apparatus the steam 
passes down through the vertical supply pipe S, 
closed at the lower end, and escapes from perfora- 
tions near the bottom to bubble up through the 
water contained in the chamber A and is carried 

away in the pipe D. In this way the steam can be made to lose enough 
heat to the water to reduce the superheat. No valves or other devices 
that have a tendency to throttle the steam and consequently superheat 
it should be placed between the saturating drum and the steam cylinder 
in which the thermometers are to be calibrated. 

A most excellent method for making calibrations of thermometers by 
means of a steam drum is a combination of the last two methods de- 
scribed. That is, the corrections are calculated from the temperature 

1 Since thermometers are calibrated usually only for increasing temperatures, the 
gage corrections to be applied should be those corresponding to increasing pressures. 
If only the average corrections of the gage are available for comparison, then the gage 
should be tapped lightly on the back of its casing when each observation is taken. 
Jarring has the effect of eliminating to some extent the lagging effects due to friction, 
which are presumably eliminated entirely when readings are taken with both increas- 
ing and decreasing pressures. 




Fig. 44. — Device to Re- 
duce the Superheat in 
Steam. 



36 POWER PLANT TESTING 

corresponding to the corrected gage pressure, and are at the same time 
checked by comparison with a " standard " thermometer. 

In all experimental work in engineering such methods of checking 
results cannot be too highly commended. Checking not only assists in 
the elimination of errors of observation as well as in calculations, but 
for the engineer it is his key to success. 1 

Observations should be tabulated in the form given on page 37. 
The column under the heading " Standard Thermometer " is to be left 
blank, of course, when only the steam gage is used for the calibration. 
To obtain the absolute pressure the barometric pressure must be observed 
during the calibration. 

Curves. 1. Plot a curve for each thermometer showing observed 
temperatures of the thermometer tested (abscissas) and the correspond- 
ing " true " or " standard " temperatures (ordinates). This curve is of 
no value, however, unless a reasonably large scale is used. 

2. Plot an error curve, taking observed temperatures of thermometer 
tested for abscissas and " errors " for ordinates. Compare with Fig. 33. 

Correction for " Stem Exposure " of Mercury Thermometers. When 
a considerable portion of the mercury column of a thermometer measuring 
high temperatures is exposed to the air, a correction K must be added to 
the readings to obtain the true temperature. If t is the observed read- 
ing, D is the number of degrees on the scale from the surface of the oil 
or mercury in the thermometer well to the end of the mercury column, 
and t' is the temperature of the air surrounding the thermometer stem, 
then for temperatures in Fahrenheit degrees, 

K = .000,088 D (t - tO (2) 

This equation, it will be observed, includes three factors: coefficient of 
expansion, length, and temperature difference. The coefficient of ex- 
pansion given in the equation is the difference between the volumetric 
coefficient of expansion of mercury (.000, 100) 2 and the linear coefficient 
(.000,012) of the kind of glass ordinarily used for thermometers. 

Recent work by Reimbach 2 shows that this equation is not quite 
accurate, particularly for comparatively short stem exposures. His 
determinations are given for Jena glass thermometers with degree gradu- 
ations about 2V mcn long in Figs. 45 and 46. Fig. 45 is for thermometers 
with the ordinary type of solid stem, that is, with the scale on the stem. 
Fig. 46 is for " sleeve " thermometers with a capillary tube enclosed in 
an outer glass tube, which covers also the scale. 

1 The plotting of curves is still another means which the engineer uses continually 
for checking his calibrations, his tests, and his conclusions. It has been well said that 
"the physician buries his mistakes but that the mistakes of the engineer bury him." 

2 Zeit.f. Inst, vol. 10 (1900). 



MEASUREMENT OF TEMPERATURE 



37 



CALIBRATION OF THERMOMETER BY COMPARISON WITH TEMPER- 
ATURES CORRESPONDING TO STEAM PRESSURES 
Record: 

1. Date and names of observers 

2. No. and type of gage 

3. No. of standard thermometer 

4. Identification of thermometer tested 

5. Limits of graduation of both 

6. Barometer reading ins. mercury = lbs. per sq. in 



Observed 
Temperatures. 



Pressures. 
Lbs. per sq. in. 



O CD 






o o° 









1 When the sign is +, the correction ("error") should be added, and when — , 
should be subtracted from the observed reading. 

Beyond the limits of the curves the equation on the preceding page 
should be used. One precaution should be noted to explain discrepancies. 
When equation (2) is used, t' is the temperature of the exposed stem, 
usually obtained by tying a very short thermometer to the stem of the 
one being calibrated. Reimbach's data were obtained by observing the 
temperature corresponding to t' with an " auxiliary " thermometer, 
having its bulb about four inches away from and on a level with the 
mid-point of the exposed stem. In the use of the equation and the 
curves for stem corrections the difference in the methods of observing 
t' must not be overlooked. 

Example. The observed thermometer reading is 500 degrees, temperature of the 
stem is 70 degrees, and immersion is up to 300 degrees. All temperatures Fahrenheit. 



38 



POWER PLANT TESTING 



Stem correction by formula (2) is 

K = .000088 X 200 (500 - 70) = 7.57 degrees. 
Corrected reading is 500 + 7.57 or nearly 507.6 degrees Fahrenheit. 



o l 
























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^ 




















^i£ 








































































"~ tpjL 


JySa*- 






















50^. — 






















20° 

10° 





100° 150° 200° 250° S00° 350° 400° 

x Difference between Reading of Thermometer and Room" Temperature in Degrees Fahr. 

Fig. 45. — Exposure Corrections for Thermometers with a Solid Stem. 

























ffft 


^ 


"8 




















■ 

2^ 


^ 




£ c 

< 

Si 




















^s5> 






3 4 

u 

1 


























bo 
ft 




















^oj£. 


80° E 


kpsssL 


.a 2 

I 

3 1 






















3?~ 




















3Qf_ 

_2iil_ 
_L0° 






100° 150° 200° 250° 300° 350 400 

Difference between Reading of Thermometer and "Room" Temperature in Degrees Fahr. 

Fig. 46. — Exposure Corrections for Thermometers of the "Sleeve" Type. 

In practice for carefully conducted tests of engines or turbines opera- 
ting with superheated steam corrections as indicated should always be 
added to the thermometer readings to obtain the correct temperature 



MEASUREMENT OF TEMPERATURE 39 

and superheat. In steam turbine tests, when a high degree of super- 
heat is used, this correction is often as much as from 5 to 10 degrees 
Fahrenheit. 

Recording Thermometers. Recently instruments for recording auto- 
matically low as well as high temperatures have been very satisfactorily 
developed. A typical example is shown in Fig. 47. It consists of a 




Fig. 47. — Typical Recording Thermometer with Flexible Tube. 

sensitive bulb (Fig. 48) suitable for being inserted into a pipe fitting and 
is attached by a capillary connecting tube to the recording instrument. 
The sensitive bulb and capillary tube are filled with either mercury or 
ether, which is sealed in the bulb and tube under pressure. The instru- 
ment is operated by the expansion of the vapor of these liquids. 

Vapor thermometers consist essentially of a metal bulb partly filled 
with a liquid which, when heated, gives off a vapor which exerts a pressure 



40 



POWER PLANT TESTING 



on a pressure gage through a small capillary tube. The following liquids 
are used, depending on the range of temperature : 

Liquid sulphur dioxide (S0 2 ) 15 to 200 degrees Fahrenheit. 

Ether (free of water) 95 to 250 degrees Fahrenheit. 

Water 212 to 450 degrees Fahrenheit. 

Heavy hydrocarbons 410 to 700 degrees Fahrenheit. 

Mercury 650 to 1350 degrees Fahrenheit. 




miimmimutmminmm 



Fig. 



Fig. 48. — "Sensitive" Bulb for a Recording Thermometer. 

The capillary tube may be made 
100 feet long, and such instruments 
are suitable for " distant reading," 
but varying the temperature of 
the capillary tube by exposure will 
alter the observations. The whole 
length of the bulb must be exposed 
to the temperature to be measured, 
and complete immersion of the 
bulb is sometimes difficult in lines 
of piping of small size. In instru- 
ments using mercury vapor the 
bulb has a volume of about one 
cubic inch in outside dimension 
per 100 degrees Fahrenheit range 
of temperature. Those filled with 
ether are of about half the volume 
required for mercury. 

One of these instruments is 
shown in Fig. 49 with the cover 
removed so that the mechanism 
can be seen. It is exactly the 
same as that of a recording pres- 
sure gage (see page 13). 




49. — Mechanism of 
Thermometer. 



Recording 



MEASUREMENT OF TEMPERATURE 41 

In general appearance and in the operation of the recording mechanism 
and clockwork, these recording thermometers are like the recording- 
pressure gages now in general use. Some of these recording instruments, 
Fig. 50, have a short rigid connection between the bulb and the record- 
ing mechanism, making it necessary to locate the instrument always 
immediately adjacent to the bulb. In Fig. 47 there is a flexible connec- 
tion of capillary tubing attached to bulb permitting the setting up of the 




Fig. 50. — Recording Thermometer, Short Bulb Type. 

instrument on a wall near by. This capillary tube must, however, be 
handled very carefully to prevent causing a serious leak, making the 
instrument useless. 

Pyrometers. Temperatures over 600 degrees Fahrenheit are usually 
measured by instruments known as pyrometers. Various types are in 
use particularly for the measurement of temperatures in flues and chim- 
neys of boiler plants. 

Thermo-electric Pyrometers. When two wires of different metals 
are joined at both ends, so as to form a complete metallic circuit, as in 
Fig. 51, and if the two junctions H (hot) and C (cold) are at different 



42 



POWER [PLANT TESTING 




Fig. 51. — Diagram Illustrat 
ing Action of a Thermo 
couple. 



temperatures, an electro-motive force is generated which can be measured 
with a galvanometer or commercial milli-voltmeter. If the cold junc- 
tion is always maintained at a constant temperature the scale of the 
galvanometer can be graduated to read di- 
rectly the temperature of the hot junction. 
In practice it is usually impracticable to main- 
tain a constant temperature at the cold junc- 
tion so that usually a compensating device is 
arranged to eliminate the error. One of these 
devices (Fig. 52) consists of an air-tight glass 
bulb partly filled with mercury into the top 
of which a U-shaped platinum loop is fused. 
This platinum loop is long enough to extend 
into the mercury and its ends are connected 
to be in series with the thermo-couple at the 
cold junction. When the temperature ' of the leads or outside circuit 
falls, the voltage due to the couple increases because of the greater 
range of temperature at the " hot junction," but the mercury in the 
bulb contracts so that the current must pass 
through a greater length of the high-resist- 
ance platinum wire in the loop. The net 
effect is that the increased resistance neu- 
tralizes the greater voltage produced at the 
" hot junction." Another method of com- 
pensation is to attach a small mercury 
thermometer to the cold couple and put a 
wire resistance in series with the circuit, 
which can be cut out in varying amounts 
by adjusting a lever on a dial graduated to 
make the resistance correspond to the tem- 
perature. 

There are two general types of such in- 
struments (1) high resistance; (2) low re- 
sistance. The high-resistance type has a couple formed of two wires 
of small diameter. One wire is of platinum and the other is an alloy 
of 90 per cent platinum and 10 per cent rhodium. 1 To protect the 
fine and delicate wires against breakage and also because platinum 
deteriorates in the silicon, phosphorus and other " gases of reaction," 
the couples of the high-resistance type are always protected by porcelain 
or iron tubes. If the temperature never much exceeds 1500 degrees 
Fahrenheit iron tubes are satisfactory. For higher temperatures porce- 

1 Formerly iridium was used for alloying but it volatilizes rapidly at over 1500 deg. 
Fahr,, causing a gradual lowering of the voltage produced. 




Fig. 52. — Mercury 

ting Device for Thermo-couples. 



MEASUREMENT OF TEMPERATURE 43 

lain tubes are used, but they must be handled carefully as they are easily 
cracked. Base-metal or low-resistance types of couples are usually 
made of alloys of nickel, iron, and copper. Couples used very largely in 
America for temperatures up to about 1500 degrees Fahrenheit are made 
of nickel-steel and copper; another is made of one wire of nickel and the 
other of an alloy of nickel and chromium. Such couples made of cheap 
metals can be made of larger rods and at less cost than the high-resistance 
type. Even though they are not quite as accurate they are generally 
preferred for industrial work. There is also the advantage that a broken 
couple can be readily replaced by rods of iron and copper fused together 
at one end. A calibration curve for the couple is easily made to be 
accurate enough for practical purposes. The principal consideration 
in selecting rods for such couples is to get them of uniform chemical 
composition and they should be annealed preferably in an electric fur- 
nace to a temperature higher than that to which they are to be exposed. 
If rods in a couple are not of uniform composition, parasitic currents are 
produced which oppose that produced by the couple at the junction. 
Since these wires can be made comparatively large, usually about ^-inch 
diameter, the current generated will be large compared with the high- 
resistance types and its change in resistance with change in temperature 
will be small, so that a cheaper low-resistance galvanometer can be used. 
Low-resistance couples are usually protected by an iron tube, mainly 
because the steel wires deteriorate in the presence of sulphur gases and 
the asbestos insulation needed for separating the rods along their full 
lengths is likely to last longer with this protection. 

Low-resistance pyrometers have often the leads of the same metals 
as the couples so that the so-called " cold-junction " is at the terminals 
of the galvanometer, and the leads are then usually made long enough to 
permit the instrument being placed where the temperature can be main- 
tained at about normal " room " temperatures. Variation in the " cold 
junction " temperature from the calibration temperature produces more 
error in low-resistance than in high-resistance types. 

When iron is a constituent of a couple, it should not be used for tem- 
peratures above 1300 to 1400 degrees Fahrenheit as this temperature is 
a " transition point " for this metal and its physical and also its thermo- 
electric properties are changed. 

Thermo-couples made of platinum and a platinum-nickel alloy pro- 
duce twice the voltage of a platinum-rhodium combination, but it should 
not be subjected to temperatures above 2000 degrees Fahrenheit. If 
the couple is made of one wire of pure platinum and another of an alloy 
of platinum and about ten per cent of rhodium, temperatures nearly as 
high as the melting point of platinum, or nearly 3500 degrees Fahren- 
heit, can be measured, although 3000 degrees Fahrenheit is considered 



44 



POWER PLANT TESTING 



the safe limit. This pyrometer with a platinum " couple " is known 
generally as a Le Chatelier type (Fig. 53). 

Electrical Resistance Thermometers are based on the principle that 
the electrical resistance of some metals increases considerably as the 
temperature is raised. Platinum is usually selected because for a given 
temperature it has a remarkably constant resistance and it does not 
deteriorate at high temperatures. A resistance thermometer of the 
simplest type is made of a coil of pure annealed platinum wire W wound 
upon a mica framework (Fig. 54) in " series " with a very small coil in a 
casing C intended to be exposed to the temperature to be measured. 
The variation of resistance is measured by a Wheatstone's bridge method. 




Fig. 54. — Resistance Thermometer 



Fig. 53. — Le Chatelier Pyrometer. 



The current from one electric battery passes through the wire in C, and 
the current from another battery passes through the coil W in the cover 
of the box. When the two circuits are connected so that the electro- 
motive forces of the two batteries are opposed, the resistance in the cover 
is adjusted by means of a connection on a stylus S so that there is no 
current passing through a telephone receiver R or a sensitive galvanom- 
eter placed at the junction of the two circuits. For making observa- 
tions this stylus is moved along the " scale " wire in the cover to a point 
where the humming noise due to the electric current ceases. The tem- 
perature can then be read on the graduated scale opposite the position of 
the stylus. 

By means of a switchboard any number of " heating " elements can 
be connected to the same indicator box, which may be located at any 
distance from the source of heat. 



MEASUREMENT OF TEMPERATURE 



45 



Commercial instruments of this type are usually arranged so that the 
" bridge " indicates the temperature in degrees. Up to 1000 degrees 
Fahrenheit the error should be less than 3 V degree and at 2400 degrees 
Fahrenheit not more than \ degree. A delicate galvanometer sensitive 
for small currents is required. A large current in the necessarily small 
wires would by its own heating change the resistance and impair sensitive- 
ness. For many classes of work, particularly if there is rough usage, 
the platinum coil C must be protected by a porcelain or iron tube. This 
protection introduces a time lag, so that very delicate instruments are 
not protected by a casing. The junctions of the platinum wire of the 
thermometer with the wires going to the resistance measuring device 
must be placed in the cooler part of the circuit, where the temperature 
should be the same as when the instrument was calibrated, or com- 
pensators may be used as explained on page 42. Electric resistance 
thermometers are readily calibrated at the temperatures of melting ice, 
steam at varying pressures (from 212 to 350 degrees Fahrenheit), and 
boiling sulphur (832.5 degrees Fahrenheit). In- 
termediate temperatures are computed. 1 Metals 
like copper, tin, and zinc when pure remain at a 
quite constant temperature for about a half hour 
when cooling slowly and passing from the liquid 
to the solid state. 

Metallic or Mechanical Pyrometers (Fig. 55) 
consist essentially of two rods made of metals 
having different rates of expansion connected by 
gears and levers to rotate a pointer on a gradu- 
ated dial. Generally the rods are made of iron 
and brass, or of graphite and iron. Although 
the use of such instruments is very common they 
are generally very unreliable, and should never 
be used for temperatures above 1000 degrees 
Fahrenheit. There is always a tendency for the 
zero of the instrument to get higher with use at 
even moderate temperatures. Beckert and Wein- 
hold found that in a number of cases the zero 
changed from 200 to 400 degrees Fahrenheit in 
two months. In order to obtain readings corre- 
sponding to the graduations the entire length of the tube enclosing 
the rods should be placed in the chamber of which the temperature is 
being measured. 

Calibrations of " Indicating " Pyrometers such as the thermo-electric, 
resistance, and mechanical types are best made by comparison with a 
1 Bulletin No. 7, U. S. Bureau of Standards. 




Fig. 



55. — "Mechanical' 
Pyrometer. 



46 



POWER PLANT TESTING 



special standard electric resistance thermometer of which the error is 
known and which is used only for standardizing work. The couple to 
be calibrated and the standard should be fastened together closely with 
only a sheet of asbestos between them. The two couples thus bound 
together should be put into an electric furnace in which the temperature 
can be controlled and raised very slowly. Then at different points in the 
scale, at intervals of about fifteen minutes, readings for comparison can 
be taken. If a standard resistance thermometer is not available a cali- 
bration can be made by comparison in a furnace of constant temperature 
with a good mercury thermometer. 1 Such thermometers in which the 
capillary tube contains rarefied nitrogen above the mercury can be 
obtained to measure temperatures with a fair degree of accuracy, when 
new, up to 1000 degrees Fahrenheit. 

The method of calibration suggested by the Power Test Committee 
of the A.S.M.E. is as follows: 

"Compare pyrometers for calibration at low ranges under proper con- 
ditions with a mercurial thermometer of known accuracy (both being 
placed for example in a current of hot air or flue gases of which the 
temperature is under control). Determine the errors at higher tempera- 
tures by plotting the results obtained as above on a chart, finding the 
curve of error, and continuing the curve to the higher ranges desired." 

For extremely high temperatures such as that of a boiler furnace or the 
bed of coals in a gas producer, the radiation optical and pneumatic 
pyrometers may be used. (See pages 46 to 51.) 

Pneumatic Pyrometers depend for their action on the variation of 
the flow of gases through orifices due to heating. Uehling's pneumatic 

pyrometer is shown diagrammatically 
in Fig. 56. As shown flue gas is con- 
tinuously drawn through two orifices 
A and B by a constant suction pro- 
duced by an aspirator D. So long as 
the air has the same temperature in 
passing through A as it has in passing 
through B, there is no change in the 
partial vacuum in the chamber be- 
tween the two apertures; if, however, 
the air has a higher temperature when 
passing through A than when passing 
through B, the suction or vacuum in 
the chamber between the two orifices 



1 


3 




4 


rv - — ^r 


^^ 


=—1000 




§- 800 




=— 600 




=- 400 




=— 200 




1 




JE 



Fig. 56. — Pneumatic Pyrometer. 



Usually temperatures vary considerably inside a furnace so that the couple and 
thermometer should be bound together in order to be sure they are exposed to the 
same temperature. 



MEASUREMENT OF TEMPERATURE 



47 



will increase in proportion to the difference in temperature between A 
and B, because the volume of air varies directly with the temperature. 

In the application of this principle orifice A is located in a nickel tube 
which is exposed to the heat to be measured, while orifice B is kept at 
a uniformly lower temperature. Filters are provided for keeping the 
orifices clean. The instrument can be made to record and indicate the 
temperature at a distance. In order to maintain a constant vacuum or 
suction at B the steam pressure at the nozzle D must be maintained 
constant by means of a good reducing valve or other means. 

Recording Pyrometers are ffiost frequently of the type of recording 
thermometers illustrated and described on pages 39 to 41. Such instru- 




Fig. 57. — Combined Indicating and Recording Pyrometer. 



ments can be constructed, when the sensitive bulb is filled with a gas 
instead of a liquid, to register accurately temperatures as high as 1200 
degrees Fahrenheit. 

Another type operated by the expansion of the vapor of mercury is 
shown in Fig. 57. This is a combined indicating and recording instru- 
ment. The sealed tube A is to be inserted in the chimney or flue in which 
the temperature is to be observed. 

Radiation Pyrometers. For temperatures above 2500 degrees Fahren- 
heit radiation pyrometers similar to the one illustrated in Figs. 58, 59 
and 60 are most suitable. They can also be used in many places where 
it is almost impossible to locate a pyrometer of any of the other types. 



48 , POWER PLANT TESTING 

The principle of operation is that the energy radiated by a so-called 
" black " body is proportional to the fourth power of its absolute tem- 
perature. The instrument illustrated consists of a cylindrical case set 
upon a tripod. This case contains a concave mirror and a lens (or 
lenses) which when properly adjusted and focused on a hot body concen- 




Fig. 58. — An Optical (Radiation) Pyrometer in Use. 

trate the heat rays upon a small thermo-electric couple 1 inside the case. 
Copper wires connect this couple with a very sensitive portable galva- 
nometer (Fig. 59) located where it can be read conveniently. The most 

1 Some of these instruments have a metal coil made up of a pair of strips of metal 
of widely different coefficients of expansion which replaces the thermo-couple. The 
principle is the same as in the metallic pyrometers (page 45). 



MEASUREMENT OF TEMPERATURE 



49 



modern instruments of this kind are provided with scales indicating 
directly degrees of temperature. Fig. 60 shows a section of the telescope 
used in connection with this pyrometer. The concave mirror M receives 
the heat rays and focuses them at F, where a small thermo-couple is 
located. To assist in pointing the telescope an eye-piece E is provided 
through which a reflected image of the hot body can be seen. The rack 
R and the pinion P, moved by a thumbscrew outside the case, serve for 
adjusting the focus of the mirror. In the center of the field of view, as 
seen in the eye-piece, the thermo-couple is seen as a black spot, and this 
must be overlapped on all sides by the image of the hot body to obtain 
the correct temperature. It is interesting to observe that the distance 
of the telescope from the source of heat does not affect the reading of the 




59. — Sensitive Galvanometer of 
Fery Radiation Pyrometer. 




Telescope of Fery Radiation 
Pyrometer. 



instrument. When the telescope gets nearer the hot body the mirror M 
receives of course more heat, but at the same time this greater amount 
of heat is distributed over a larger image and the intensity of the heat 
remains the same. 

Radiation pyrometers are calibrated in terms of the radiation from a 
so-called " black body," which is approximately realized by a uniformly 
heated enclosure. It is only for " black bodies," such as carbon, coal, 
etc., that the temperature is exactly proportional to the fourth root of 
the heat energy. Readings obtained when measuring the temperature 
of a body not inside a closed chamber with hot walls will in some cases 
be very much lower than the true temperature. For a piece of heated 
coal the error is very small due to lack of enclosure, while in the case of 
molten copper or tin with a clean surface the temperature reading may 
be 100 degrees Fahrenheit too low. Conditions as regards enclosure are, 



50 POWER PLANT TESTING 

however, satisfactory in most practical cases where the instrument is 
frequently used, such as taking the temperature of boiler furnaces, gas 
producers and retorts, annealing and hardening furnaces, etc. Error 
due to the furnace door being open for an instant when the observation 
is to be made is practically negligible, especially as these instruments 
are actually calibrated under this condition. If excess of air in a fur- 
nace is likely to reduce the temperature while sighting, a large tube of 
cast iron or fire-clay closed at the end toward the fire can be built into 
the furnace wall. By sighting through the open end upon the closed 
end which should be at the furnace temperature very satisfactory results 
are obtained. 

Observations made with such pyrometers of incandescent bodies or 
gases do not give the true temperature. It is generally assumed, how- 
ever, that they can be used to measure fairly accurately the temperature 
of heated chambers when focused upon the walls, 1 because of the reflec- 
tion going on in all directions. In most cases the flame temperature 
can be taken the same as that of the surrounding walls. 

A relatively large area is usually required to sight radiation pyrometers. 
It is stated that the distance from the telescope to the hot body can be 
as much as 30 times the diameter of the hot body and the telescope can 
be taken as much nearer as desired without changing the reading of 
instrument. Before taking observations the pointer of the galvanom- 
eter must be set at zero, the instrument receiving no heat rays during 
this adjustment. The readings of temperature made with such instru- 
ments are obviously the difference between the temperatures of the hot 
body and of the room. 

Optical Pyrometers. Another type of pyrometer, based in principle 
upon the measurement of the brightness of the hot body by comparison 
with a standard lamp, is shown in Fig. 61. In order to use this instru- 
ment, known as Wanner's, the incandescent (osmium filament) lamp 
must first be standardized by comparison with an amylacetate oil lamp 
of constant candle power. Then after standardizing it is only necessary 
to focus the instrument upon the hot body to be measured and the tem- 
perature is read directly on the graduated scale at the eye-piece. 

Temperature readings from optical pyrometers are actual and are not 
differences depending on the temperature of the room. 

Both the Fery and Wanner pyrometers have a satisfactory range from 
800 to 4000 degrees Fahrenheit. At the lower temperatures the average 
error of such instruments is about 3 degrees Fahrenheit and the maxi- 
mum error at temperatures above 3000 has been shown to be not more 
than 20 degrees. 

1 " Heat Energy and Fuels," by Hanns von Juptner, page 76. 



MEASUREMENT OF TEMPERATURE 



51 



Furnace temperatures can be determined approximately from the values correspond- 
ing to the color of the fire. All temperatures are in degrees Fahrenheit. 

Red — just visible 900 Orange 2000 

Dull red 1250 White 2350 

Cherry red 1600 Dazzling white 2700 

Radiation and optical pyrometers are invaluable for determining the 
temperatures of the various parts of a furnace, of the walls of the setting 
of a steam boiler, of various portions of a bed of coals, etc. It is some- 
times stated that an optical pyrometer is a means for measuring tem- 
peratures of objects " miles away." 

Diffusing Glass -f%jj j — "f*j " 

Flame 
Gage 




Fig. 61. — Wanner Optical Pyrometer in Position for Standardizing. 

Calorimetric Pyrometers. If the specific heat and weight of a body 
are known, its temperature can be obtained by observing the rise in 
temperature of a known quantity of water into which the body is thrown. 

More in detail the method consists in the determination of temperature 
by putting a ball of metal or other refractory material into the medium 
of which the temperature is to be measured. When the ball has become 
heated uniformly throughout its mass to the temperature of the medium 
it is transferred quickly to a cup heavily jacketed with non-conducting 
material in which there is a known weight of water at a known tem- 
perature. Copper, wrought iron and fire-clay are suitable materials. 
Specific heats of these materials at about 500 degrees Fahrenheit are 
respectively .097, .110 and .180. Since metals are readily attacked by 
furnace gases they should be protected when used in this way in a cru- 
cible of refractory material. 

This method is often very serviceable in places or at times when 
accurate pyrometers are not available. On account of the " personal " 
error liable to enter, such determinations should be repeated several 
times to check the results. Calculations required are as follows. 1 

1 A more complete description of calorimetric pyrometers and the precautions to 
be observed for accuracy will be found in Transactions of the American Society of 
Mechanical Engineers, vol. VI, page 712. 



52 



POWER PLANT TESTING 



Let Wi = weight of the ball, pounds. 

w 2 = weight of the cup (only the " inner " vessel), 1 pounds. 

w 3 = weight of the water in the cup, pounds. 

ti = initial temperature of water, degrees Fahrenheit. 

t 2 = final temperature of the water, degrees Fahrenheit. 

to = temperature of the heated ball, degrees Fahrenheit. 

Si = specific heat of the ball. 

s 2 = specific heat of the cup. 



Then 



W1S1 (t 



t 2 ) 
to 



(W 2 S 2 + W 3 ) (tj - ti), 

(w 2 S 2 + W 3 ) (tg - ti) 
W1S1 



+ t 2 



(2) 



Seger Pyrometer Cones. For many purposes when a pyrometer 
cannot be well placed fusible Seger cones are used. Such cones are 
made of several different oxides mixed in a manner to give a definitely 
known melting point for each one. The melting points range from 590 
degrees to 1850 degrees Centigrade by steps of from 20 to 30 degrees, 
each having a standard number. These cones are carefully graded, so 
that if one has had some experience with them, temperatures can be 
estimated to about the nearest ten degrees in Centigrade. Four of these 
cones are shown in Fig. 62. 




Fig. 62. — Seger Cones after Use. 

When a series of cones is placed in a furnace the one having the lowest 
melting point begins to turn over first. The temperature corresponding 
to the cone number is reached when the tip of the cone has bent over and 
just touches the surface on which it is standing. Hence the highest 
temperature reached when the cones shown in the illustration were used 
was about half way between that corresponding to each of the two 
middle cones. According to the numbers on the cones the temperature, 

1 It would be more accurate, of course, to use in the calculation the water equiva- 
lent of the whole vessel, as is done in coal calorimetry. See page 210. Units given 
are in pounds and degrees Fahrenheit, but other units, provided they are correspond- 
ing, can be used in the equation given. 



MEASUREMENT OF TEMPERATURE 



53 



as given by the following table, was between 830 and 860 degrees Centi- 
grade. The greatest disadvantage with this system is that there is no 
way of observing a decrease in the temperature, or, in other words, only 
the maximum temperature is indicated.^ 

The following table gives the temperatures, in degrees Centigrade, 
at which the Seger cones will begin to melt: 



Seger 


Temp. 


Seger 


Temp. 


Seger 


Temp. 


Cone No. 


Deg. C. 


Cone No. 


Deg. C. 


Cone No. 


Deg. C. 


022 


590 


04 


1070 


15 


1430 


021 


620 


03 


1090 


16 


1450 


020 


650 


02 


1110 


17 


1470 


019 


680 


01 


1130 


18 


1490 


018 


710 


1 


1150 


19 


1510 


017 


740 


2 


1170 


20 


1530 


016 


770 


3 


1190 






015 


800 


4 


1210 


26' 


i650'' 


014 


830 


5 


1230 


27 


1670 


013 


860 


6 


1250 


28 


1690 


012 


890 


7 


1270 


29 


1710 


011 


920 


8 


1290 


30 


1730 


010 


950 


9 


1310 


31 


1750 


09 


970 


10 


1330 


32 


1770 


08 


990 


11 


1350 


33 


1790 


07 


1010 


12 


1370 


34 


1810 


06 


1030 


13 


1390 


35 


1830 


05 


1050 


14 


1410 


36 


1850 



Two types of mercury thermometers protected by heavy metal cases 
are illustrated by Figs. 63 and 64. It will be observed that a very satis- 
factory thermometer well is a part of the casing. The one shown in 
Fig. 64 has graduations for reading both temperatures and pressures. 
A thermometer of this type is particularly useful in pipes carrying hot 
boiler feed-water. When the temperature is above 212 degrees Fahren- 
heit the thermometer will indicate that the water is being heated at a 
pressure higher than atmospheric. For water heated in closed vessels 
or pipes there is for every temperature a corresponding pressure as given 
in tables of the properties of saturated steam. 1 

Relative Accuracy of Thermometers and Pyrometers. For low- 
temperature work mercury thermometers are generally preferred as they 
can be made to almost any degree of accuracy required. For tempera- 
tures above 500 degrees Fahrenheit electric resistance thermometers 
and pyrometers come into use. When provided with a delicate galva- 
nometer electric resistance thermometers can be used with a very high 
degree of accuracy, and in fact temperature differences can be determined 
with them very much more accurately than with the best mercury ther- 

1 Short and very much abbreviated tables of the properties of saturated steam are 
given in the Appendix. 



54 



POWER PLANT TESTING 



mometers. Next in degree of accuracy are probably thermo-electric 
pyrometers; and it is interesting that a pyrometer of this kind can be 
readily made by twisting together at their ends, rods of wrought iron and 



Fig. 63. - — Combined Thermometer 
Well and Protective Casing. 



Fig. 64. — Combined Thermometer and 
Pressure Gage for Boiler Feed-water Pipes. 



nickel. It is not essential that the ends should be welded but welding 
(preferably electric) gives the couple greater permanency, by preventing 
the accumulation of dust interfering with electrical conductivity. The 
loose ends can be connected up to the binding posts of a millivoltmeter 
by insulated copper wires and calibrated. The only disadvantage will 
be that it will not have a scale reading directly in degrees of temperature. 
The wrought-iron and nickel rods should be covered with a winding of 
asbestos tape to keep them separated. Mechanical pyrometers are not 
very accurate. Optical and radiation pyrometers have a special field 
beyond the limits of the other types. 



CHAPTER III 



DETERMINATION OF THE MOISTURE IN STEAM 



Unle33 the steam used in the power plant is superheated it is said to 
be either dry or wet, depending on whether or not it contains water in 
suspension. The general types of steam calorimeters, used to determine 
the amount of moisture in the steam, may be classified under three heads : 

1. Throttling or superheating calorimeters. 

2. Separating calorimeters. 

3. Condensing calorimeters. 

Throttling or Superheating Calorimeters. The type of steam calorim- 
eter used most in engineering practice operates by passing a sample of 
the steam through a small ori- 
fice, in which it is superheated 
by throttling. A very satis- 
factory calorimeter of this kind 
can be made of pipe fittings as 
illustrated in Fig. 65. It con- 
sists of an orifice O, discharg- 
ing into a chamber C, into 
which a thermometer T is in- 
serted, and a mercury manom- 
eter is usually attached to the 
cock V 3 , for observing the pres- 
sure in the calorimeter. 

It is most important that all 
parts of calorimeters of this 
type, as well as the ■ connec- 
tions leading to the main steam 
pipe, should be very thoroughly 
lagged by a covering of good 
insulating material. One of the 
best materials for this use is 
hair felt, and it is particularly well suited for covering the more or less 
temporary pipe fittings, valves, and nipples through which steam is 
brought to the calorimeter. Very many throttling calorimeters have 
been declared useless by engineers and put into the scrap heap merely 
because the small pipes leading to the calorimeters were not properly 
lagged, so that there was too much radiation, producing, of course, con- 

55 




Fig. 65. — Simple Throttling Calorimeter. 



56 POWER PLANT TESTING 

densation, so that the calorimeter did not get a true sample. It is obvi- 
ous that if the entering steam contains too much moisture the drying 
action due to the throttling in the orifice may not be sufficient to super- 
heat. It may be stated in general that unless there is about 5 to 10 
degrees Fahrenheit of superheat in the calorimeter, or in other words 
unless the temperature on the low-pressure side of the orifice is at least 
about 5 to 10 degrees Fahrenheit higher than that corresponding to 
the pressure in the calorimeter, there may be some doubt as to the 
accuracy of results. 1 The working limits of throttling calorimeters vary 
with the initial pressure of the steam. For 35 pounds per square inch 
absolute pressure the calorimeter ceases to superheat when the percentage 
of moisture exceeds about 2 per cent; for 150 pounds absolute pressure, 
when the moisture exceeds about 5 per cent ; and for 250 pounds absolute 
pressure, when it is in excess of about 7 per cent. For any given pressure 
in the main the exact limit varies slightly, however, with the pressure in 
the calorimeter. 

In connection with a report on the standardizing of engine tests, the 
American Society of Mechanical Engineers 2 published the following 
instructions regarding the method to be used for obtaining a fair sample 
of steam from the main pipes. It is recommended in this report that 
the calorimeter shall be connected with as short intermediate piping as 
possible with a so-called calorimeter sampling nozzle made of |-inch 
pipe and long enough to extend into the steam pipe " nearly across to " 
the opposite wall. The end of this nipple is to be closed so that the 
steam must enter through not less than twenty |-inch holes " equally 
distributed from end to end and preferably drilled in irregular or spiral 
rows, with the first hole not less than f-inch from the inner wall of the 
pipe." 

"The sampling nozzle should not be placed near a point where water 
may pocket or where such water may affect the amount of moisture con- 
tained in the sample. Where non-return valves are used, or where there 
are horizontal connections leading from the boiler to a vertical outlet, 
water may collect at the lower end of the uptake pipe and be blown up- 
ward in a spray which will not be carried away by the steam owing to a 

1 The same general statement may be made as regards determinations of super- 
heat in engine and turbine tests. Experience has shown that tests made with from 
to 10 degrees Fahrenheit superheat are not reliable, and that the steam consumption 
in many cases is not consistent when compared with results obtained with wet or more 
highly superheated steam. The errors mentioned, when they occur, are probably due 
to the fact that in steam, indicating less than 10 degrees Fahrenheit superheat, water 
in the liquid state may be taken up in " slugs" and carried along without being entirely 
evaporated. 

2 Transactions American Society of Mechanical Engineers, vol. 21; and the Journal, 
Nov., 1912, pages 1713-14. 



DETERMINATION OF THE MOISTURE IN STEAM 57 

lack of velocity. A sample taken from the lower part of this pipe will 
show a greater amount of moisture than a true sample. With goose- 
neck connections a small amount of water may collect on the bottom of 
the pipe near the upper end where the inclination is such that the ten- 
dency to flow backward is ordinarily counterbalanced by the flow of 
steam forward over its surface; but when the velocity momentarily 
decreases the water flows back to the lower end of the goose-neck and 
increases the moisture at that point, making it an undesirable location 
for sampling. In any case it should be borne in mind that with low 
velocities the tendency is for drops of entrained water to settle to the 
bottom of the pipe, and to be temporarily broken up into spray whenever 
an abrupt bend or other disturbance is met." 

If it is necessary to attach the sampling nozzle at a point near the end 
of a long horizontal run, a drip pipe should be provided a short distance in 
front of the nozzle, preferably at a pocket formed by some fitting, and 
the water running along the bottom of the main drawn off, weighed, and 
added to the moisture shown by the calorimeter, or better, a steam sepa- 
rator should be installed at the point noted. 

In testing a boiler the sampling nozzle should be located as near as 
possible to the boiler, and the same is true as regards the thermometer 
well when the steam is superheated. In a turbine or engine test these 
locations should be as near as practicable to the throttle valve. In the 
test of a plant where it is desired to get complete information, especially 
where the steam main is unusually long, sampling nozzles or thermometer 
wells should be located at both the boiler and the engine, so as to obtain 
as complete data as may be required. The sample of steam should 
always be taken from a vertical pipe as near as possible to the engine, 
turbine, or boiler being tested. Good examples of calorimeter nipples 
are illustrated in Figs. 67 and 74. 

Never close and usually do not attempt to adjust the discharge valve 
V 2 (Fig. 65) without first closing the gage cock V 3 . Unless this pre- 
caution is taken the pressure may be suddenly increased in the chamber 
C, so that if a manometer is used the mercury will be blown out of it, 
and if, on the other hand, a low-pressure steam gage is used it may be 
ruined by exposing it to a pressure much beyond its scale. 

Usually it is a safe rule to begin to take observations of temperature 
in calorimeters after the thermometers have indicated a maximum value 
and have again receded slightly from this maximum. 

The quality or relative dryness of wet steam is easily calculated by 
the following method. Using the symbols, 

pi = steam pressure in main, lbs. per sq. in. abs. 

P2 = steam pressure in calorimeter, lbs. per sq. in. abs. 

t c = temperature in calorimeter, deg. Fahr. 



58 POWER PLANT TESTING 

T] and qi = heat of vaporization, and heat of liquid corresponding 

to pressure pi, B.t.u. per pound. 
H 2 and t 2 = total heat (B.t.u.) and temperature (deg. Fahr.) corre- 
sponding to pressure p 2 . 
c p = specific heat of superheated steam. Assume 0.46 for low 

pressures existing in calorimeters. 1 
Xi = initial quality of steam (a decimal). 
ioo (i — Xi) = initial moisture in steam, per cent. 

Total heat in a pound of wet steam flowing into the orifice is 

xir x + qi, 

and after expansion, assuming all the moisture is evaporated, the total 
heat of the same weight of steam is 

H 2 + c p (t c - t 2 ). 

Then assuming no heat losses and putting for c p its value 0.46 we have, 

Xtfi + qi = H 2 + 0.46 (t c - ;ta), (3) 

H 2 + 0.46 (t c - t a ) - q, . ,, 

or Xi = ^ (3') 

Ti 

Charts for Moisture Determinations. A small section of the total- 
heat-entropy chart as provided in modern steam tables is shown in Fig. 
66. It is arranged particularly for determinations of the quality of 
steam with a throttling calorimeter without using the equations above. 
Horizontal lines in the chart are those of constant total heat of the steam, 
and represent the process in a throttling calorimeter. To illustrate the 
application of the chart let the initial pressure of steam be 165 pounds 
per square inch absolute and the reading of the thermometer on the 
low-pressure side of the calorimeter be 270 degrees Fahrenheit. The 
pressure in the calorimeter is 15.2 pounds per square inch absolute. 
To find the quality x start at the intersection of the temperature line for 
270 degrees with the 15.2 pounds pressure line and go across the chart 
horizontally to the 165 pounds line, then the " lines of constant quality" 
indicate that the quality of the steam is 0.979. 

When a U-tube manometer is used to determine the pressure in a 
calorimeter of the type illustrated in Fig. 65, this pressure can be obtained 
very accurately, and an excellent means is provided for calibrating the 
thermometer in the calorimeter just as it is to be used. The calibration 
would be made, of course, by the method of comparing with the tempera- 
ture corresponding to known pressures explained on page 34. In order 
to avoid having superheated steam in the calorimeter for this calibration 

1 Average values for the specific heat of superheated steam for any pressures and 
temperatures are given on page 309. 



DETERMINATION OF THE MOISTURE IN STEAM 59 

the felt or similar material usually needed for covering the valves and 
nipples between the main steam pipe and the calorimeter should be kept 
saturated with cold water. 

The Barrus Throttling Calorimeter. An important variation from 
the type of throttling calorimeter shown in Fig. 65 has been introduced 
quite widely by Mr. George H. Barrus. In this apparatus the tempera- 
ture of the steam admitted to the calorimeter is observed instead of the 
pressure and a very free exhaust is provided, so that the pressure in 
the calorimeter is atmospheric. This arrangement simplifies very much 




Fig. 



Entropy 

Chart for Determining Quality of Steam with any Throttling Calorimete 



the observations to be taken, as the quality of the steam Xi can be calcu- 
lated by equation (3') by observing only the two temperatures ti and t c , 
taken respectively on the high- and low-pressure sides of the orifice in the 
calorimeter. This calorimeter is illustrated in Fig. 67. The two ther- 
mometers required are shown in the figure. Arrows indicate the path 
of the steam. 1 

The orifice in such calorimeters is usually made about ^V inch in 
diameter; and for this size of orifice the weight of steam 2 discharged per 

1 Transactions American Society of Mechanical Engineers, vol. 11, page 790. 

2 Formulas for calculating the exact weight of steam discharged from a nozzle are 
given on pages 189 and 190. In boiler-tests corrections should be made for the steam 



60 



POWER PLANT TESTING 




Fig. 67. — Barrus Throttling Steam Calorimeter. 



hour at 175 pounds per square inch absolute pressure is about 60 pounds. 
It is important that the orifice should always be kept clean, because if it 
becomes obstructed there will be a reduced quantity of steam passing 

through the instrument, 
making the error due to 
radiation relatively more 
important. 

In order to free the ori- 
fice from dirt or other ob- 
structions the connecting 
pipe or calorimeter nipple to 
be used for attaching the 
calorimeter to the main 
steam pipe should be blown 
out thoroughly with steam 
before the calorimeter is put 
in place. The connecting 
pipe and valve should be 
covered with hair felting not 
less than f inch thick. It is desirable also that there should be no leak 
at any point about the apparatus, either in the stuffing box of the sup- 
ply valve, the pipe joints, or in the union. 

Fig. 68 is a diagram for the determination of the quality of steam 
which is particularly suitable for use in connection with calorimeters of 
the Barrus type. 

Abscissas in this diagram are temperatures in the calorimeter t c , and 
the ordinates are the initial temperatures ti of the steam before expansion 
in the calorimeter. 

With the help of such a diagram the Barrus calorimeter is particu- 
larly well suited for use in power plants, where the quality of the 
steam is entered regularly on the log sheets. The percentage of mois- 
ture is obtained immediately from two observations without any calcu- 
lations. 

A very good design of throttling calorimeter recommended by the 
Power Test' Committee of the A.S.M.E. to be accepted as the standard 
for tests is shown in Fig. 69. The calorimeter is made practically 
throughout of ^-inch pipe fittings and has an orifice -fy inch in diameter 
in a flat plate. (Fig. 70.) This orifice is of a suitable size to throttle 
steam at the usual boiler pressures down to atmospheric. The wooden 
box should be filled with hair felt, 85 per cent magnesia, or an equally 

discharged from the steam calorimeters. The Power Test Committee of the A.S.M.E. 
suggest the use of Napier's formula, believing it to be sufficiently accurate for this 
kind of work. 



DETERMINATION OF THE MOISTURE IN STEAM 61 



Temperature in Calorimeter, Degrees Fahi". v 
240 250 260 270 280 290 300 310 













































7T " ~~ 




/-: 








ff±- ■--/:::- 












ESliEffll^ 


























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tjl^'l^r^l 




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^/: r. V j"::. 7 i :~[ ::: iiltf 


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fr :: ■ ' ; 1 : /• 






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240 250 260 270 280 290 300 310 320 <o 
Temperature in Calorimeter, Degrees Fahr. 



Fig. 68. — Chart for Determining Quality of Steam from Temperature Observations. 
(Atmospheric Pressure in Calorimeter.) 



62 



POWER PLANT TESTING 



good heat insulator. This committee states the following method of 
calculating the quality of steam with this instrument: 




Fig. 



Simple Throttling Calorimeter. (A.S.M.E.Type.) 



4-Mg x iKo Bu t ton head 
bolts hexagonal nuts 



Use \§ gaskets 
between flangeg. 



High pressure 
packing 



The percentage of moisture is determined by observing the number of degrees of 

cooling that the thermometer in the 
low-pressure steam shows as its ' nor- 
mal' reading for dry steam and di- 
viding that number by the 'constant ' 
number of degrees representing one 
per cent of moisture. To determine 
this ' normal ' reading corresponding 
to dry steam the instrument should 
be attached to a horizontal steam 
pipe in such a way that the sam- 
pling nozzle projects upward to near 
the top of the pipe, there being no 
perforations, and the steam enters 
through the open top of the nozzle. 
The test should be made when the steam in the pipe is in a quiescent state, and 




Mo Vulcanized 
Tiber Washers 



Fig. 70. — Detail of Orifice for Fig. 69. 



DETERMINATION OF THE MOISTURE IN STEAM 63 



the steam pressure is maintained constantly at the point observed on the main 
trial. If the steam pressure falls during the time the observations are being made, 
the test should be continued long enough to obtain the effect of an equivalent rise 
of pressure. ■ 

" To find the constant for one per cent of moisture divide the latent heat of the 
steam supplied to the calorimeter at the observed pressure or temperature by the 
specific heat of superheated steam at atmospheric pressure (0.46) and divide 
the quotient by 100. Finally ascertain the percentage of moisture by dividing 
the number of degrees of cooling by the 'constant' as above noted." 

Separating Calorimeters. It was explained on page 56 that throttling 
calorimeters cannot be used for the determination of the quality of steam 
when for comparatively low pressures the 
moisture is in excess of 2 per cent, and when 
for average boiler pressures in modern engi- 
neering practice it exceeds 5 per cent. For 
higher percentages of moisture than these low 
.limits separating calorimeters are most gen- 
erally used. In these instruments the water 
is removed from the sample of steam by me- 
chanical separation just as it is done in the 
ordinary steam separator installed in the steam 
mains of a power plant. There is provided, 
of course, a device for determining, while 
the calorimeter is in operation, usually by 
means of a calibrated gage glass, the amount 
of moisture collected. This mechanical sep- 
aration depends for its action on changing 
very abruptly the direction of flow and re- 
ducing the velocity of the wet steam. Then 
since the moisture (water) is nearly 300 times 
as heavy as steam at the usual pressures de- 
livered to the engine, the moisture will be 
deposited because of its greater inertia. 

One of the simplest forms of separating calorimeters, made of pipe 
fittings, is shown in Fig. 71. Steam enters at A, passes down through the 
vertical pipe P, plugged at the lower end, from which it escapes through 
a large number of |-inch holes indicated in the figure. In passing through 
these holes the direction of flow is changed very abruptly, since the steam 
must go upward to be discharged at D. Moisture is deposited at the 
bottom of the vessel V, and its volume or weight can be determined from 
the height of the water in the gage glass G if the vessel has been calibrated. 
Steam discharged from D must be condensed and weighed in a pail or 
barrel containing cold water. The percentage of moisture is then found 




Fig. 71. — A Simple Separat- 
ing Steam Calorimeter made 
of Pipe Fittings. 



64 



POWER PLANT TESTING 



by dividing the weight of water collected in the vessel V by the sum of 
the weight of steam condensed and the weight of water collected in V. 
This sum is, of course, the weight of the wet steam. 

Radiation Loss. As in all calorimetry work, in order to obtain accu- 
rate results there should be a covering of hair felt f inch thick over all 

parts of the apparatus, and 
even then the radiation loss 
is sometimes large enough to 
make corrections necessary. 
This correction is determined 
by operating two calorimeters 
which are exactly alike in con- 
struction and in the amount 
of felt covering, in series, and 
so arranged that the second 
takes the discharge of the first. 
If it is known that the dis- 
charge from the first calorim- 
eter is perfectly dry steam 1 
then the moisture collected in 
the second calorimeter is the 
condensation due to its own 
radiating surface, which should 
be the same as for the first. 
Calculations for corrected 
moisture determinations are 
made then by subtracting from 
the moisture collected in the 
first instrument the amount 
condensed in the second. 
When, of course, the radia- 
tion loss has been once deter- 
mined it is not necessary to 
operate the second calorimeter. 
Fig. 72 illustrates a form of 
separating calorimeter in which 
the improvement over the one shown in Fig. 71 is in the addition of a 
steam-jacketing space receiving live steam at the same temperature as the 
sample. Steam is supplied through a pipe A, discharging into a cup B. 
Here the direction of the flow is changed through nearly 180 degrees, 

1 A small throttling calorimeter can be attached to the discharge from the first 
separating calorimeter to determine by a separate test whether or not the steam dis- 
charged is dry, 




Fig. 



72. — Separating Steam Calorimeter 
Steam Jacket. 



with 



DETERMINATION OF THE MOISTURE IN STEAM 65 

causing the moisture to be thrown outward through the meshes of the 
cup into the vessel V. The dry steam passes upward through the spaces 
between the webs W into the top of the outside jacketing chamber J, 
and is finally discharged from the bottom of this steam jacket through 
the nozzle N. This nozzle is considerably smaller than any other section 
through which the steam flows, so that there is no appreciable difference 
between the pressures in the calorimeter proper and the jacket. The 
scale opposite the gage glass G is graduated to show in hundredths of a 
pound, at the temperature corresponding to steam at ordinary working 
pressures, the variation of the level of the water accumulating. A steam 
pressure gage P indicates the pressure in the jacket J, and since the flow 
of steam through the nozzle N is roughly proportional to the pressure 
(see page 189), another scale in addition to the one reading pressures is 
provided at the outer edge of the dial. A petcock C is used for draining 
the water from the instrument, and by weighing the water collected cor- 
responding to a given difference in the level in the gage G, the scale 
opposite it can be readily calibrated. Too much reliance should not be 
placed on the readings for the flow of steam as indicated by the gage P, 
unless it is frequently calibrated. Usually it is very little trouble to 
connect a tube to the nozzle N and condense the steam discharged in a 
large pail nearly filled with water. When a test for quality is to be made 
by this method the pail nearly filled with cold water is carefully weighed 
and then at the moment when the level of the water in the water gage G 
has been observed the tube attached to the nozzle N is immediately 
placed under the surface of the water in the pail. The test should be 
stopped before the water gets so hot that some weight is lost by " steam- 
ing." The gage P is generally calibrated to read pounds of steam flowing 
in ten minutes. For the best accuracy it is desirable to use a pail with 
a tightly fitting cover into which a hole just the size of the tube has been 
cut. 

Combined Separating and Throttling Calorimeters. Calorimeters as 
already described are effective in removing practically all the moisture 
in steam when the pressure is not lower than 25 pounds by gage. 
For lower pressures, particularly around atmospheric, recent experi- 
ments show that the efficiency of such calorimeters is in some cases not 
more than 80 per cent. 1 For this reason in the best current practice for 
determinations of moisture in low-pressure steam a throttling calorim- 
eter is attached to the" discharge of the separating calorimeter. Then 
if the separating calorimeter has been carefully calibrated for radiation 
loss and the steam escaping from the separating calorimeter is tested 

1 Transactions American Society of Mechanical Engineers, vol. 32 (1910), page 1132. 
The efficiency of the calorimeter is the ratio of the percentage of moisture taken out by 
the separating calorimeter to the total percentage of moisture. 



66 POWER PLANT TESTING 

again in a throttling instrument, it is possible to make correct determi- 
nations for the percentage of moisture in the steam of almost any degree 
of wetness. An apparatus of this kind which is reported to have done 
excellent service in tests of very large low-pressure steam turbines, oper- 
ating with the exhaust from reciprocating steam engines in New York 
city, is shown in Fig. 73. The most unique feature of this apparatus 
is the sampling tube. It was found that for this low-pressure steam the 
ordinary sampling tube of perforated pipe (see Figs. 67 and 74) did not 



\C Mercury 
Column tf n 
Connection 




Fig. 73. — Combined Separating and Throttling Steam Calorimeter. 



give a reliable sample. It was also found necessary that the sample 
should be taken from the main without changing its direction or velocity 
until it is actually inside the sampling pipe. If the direction of flow of 
wet steam is suddenly changed when entering the sampling nozzle, the 
entrained moisture, because of its greater specific gravity on the one 
hand and the very slight skin friction between it and the surrounding 
dry steam on the other, will cause it to continue in its path in a straight 
line, so that there is a tendency for only dry steam to enter the nozzle. 
Also if the velocity of the steam in the sampler is greater than that in the 



DETERMINATION OF THE MOISTURE IN STEAM 67 

main, there is a tendency for the dry steam to " accelerate " into the 
nozzle, leaving the moisture behind. It has been stated that this action 
has not been observed in tests of steam at high pressures, because (1) of 
smaller differences between the specific gravity of high-pressure steam 
and water; (2) greater skin friction; (3) the highly divided state of the 
moisture. 1 

As the throttling calorimeter is ordinarily used it would have very 
little capacity when used with steam pressures only a little above at- 
mospheric; but by making it discharge into a receiver in which a vacuum 
of about 28 inches of mercury is maintained the throttling portion of the 
calorimeter will evaporate from two to three per cent of moisture. 

The apparatus shown in Fig. 73 consists of the f-inch brass nozzle on 
the sampling tube which is bent to point in the direction opposite to 
the flow of the steam. The lip of this nozzle is filed to a knife-edge 
to avoid disturbing the current of steam around the mouth of the sampler 
by eddies and impact against a thick lip. This sampling tube is set up 
so that it extends into the main steam pipe one-sixth of the diameter of 
the pipe, where it has been observed to give practically a true average 
sample. When in operation the valve at the sampling tube is opened wide 
and the flow is regulated by means of the lever cock between the separating 
and the throttling calorimeters. The necessary throttling action ordinarily 
produced by an orifice is produced by this cock. A vacuum is maintained 
in the throttling portion from which the discharge is carried to a small 
cooling receiver in which the steam is condensed. From this receiver it 
flows to a " volumetric " measuring tank of which the top is tightly 
closed and connected by 5-inch pipes to the main condenser. A spy- 
glass shown at the left in the figure is useful for proving that the calorim- 
eter is working properly. It often happens that when the superheat 
in the calorimeter is less than from five to eight degrees Fahrenheit there 
is some moisture passing through and the spy-glass will invariably show 
it. As the spy-glass is most conveniently made of f-inch gage glass its 
area is not large enough to carry all the steam, and a by-pass connection 
is arranged as shown. The large size of the parts is necessary on account 
of the very large specific volume of the low-pressure steam. 

All parts of the apparatus are carefully covered with magnesia-asbestos 
covering 2 inches thick. For the normal rate of flow for the instrument, 
the radiation can be made less than 0.1 per cent. 

Calculation of Percentage Moisture for Combination Separating and 
Throttling Calorimeter. Quality of steam Xi is calculated for a combi- 
nation calorimeter as follows: 



1 H. G. Stott, Transactions American Society of Mechanical Engineers, vol. 32 
(1910), page 77. 



68 POWER PLANT TESTING 

Let Wi = weight of moisture collected in the separating calorimeter 

in a given time, in pounds. 
W2 = weight of dry steam condensed after passing through the 

throttling calorimeter, in pounds. 
x 2 = quality of steam discharged from separating portion as 

determined by the throttling calorimeter; 
then without sensible error, 

I - X ' = ^T^ + (I - X ' ) (4) 

and in terms of " quality " (always a decimal), we have more accurately, 1 

W 2 / A 

Xl = X2X ^Rr 2 (4) 

Still another type of combined calorimeter is illustrated in Fig. 74. 
In this instrument the sample of steam is collected by the perforated 
tube in the main steam pipe. The temperature before expansion in 
the throttling plug is indicated by the thermometer marked T x , and 
another thermometer T 2 gives the temperature after throttling. A scale 
S opposite the glass water gage G is used to show the weight of water 
separated from the steam. The proportion of moisture separated in 
relation to the total weight of wet steam passing through the instrument 
is the percentage of moisture separated. This percentage added to the 
percentage of moisture determined by throttling as calculated from the 
readings of the thermometers gives the approximate total percentage of 
moisture, as by equation (4) above. 

A calorimeter of this type is particularly useful for making tests in 
power plants where the quality of the steam may vary considerably. 
It sometimes happens that a test is started with nearly dry steam; but 
after a while something goes wrong in the boiler room, as for example too 
much water may be fed into the boilers causing " priming," and the 
throttling calorimeter becomes useless for determining the quality. If 
a separating calorimeter is at hand this may be substituted; but to make 
a change often takes some time and meanwhile some observations may 
be lost. If, however, one of these combined calorimeters is used, it will 
operate satisfactorily as a simple throttling instrument when the steam 
is nearly dry; and, without adjustment, will also take care of very wet 
steam. 

This type is also very useful to consulting engineers for making tests 

1 If the radiation test shows it is large enough to be appreciable, and if R is 
weight of condensation due to radiation in pounds in a given time corresponding to 
that for the other units, then 

„;.„ x z!±i (4 -, 

Wl +W2 



DETERMINATION OF THE MOISTURE IN STEAM 69 



at plants where there is no definite information available as to the quality 
of steam supplied by the boilers. 1 

Electric Steam Calorimeters. For use with very wet steam the 
Thomas electric calorimeter, Fig. 75, has been designed. It consists 
essentially of a cylindrical vessel B containing a series of resistance coils 
of German silver wire for heating steam by means of the electric current 
passing through them. These coils are connected to the electric terminals 
or binding-posts shown in the figure, and are supported in a soapstone 
cylinder in which there are a large number of |-inch holes through 
which the coils pass up and down. 




Perforated Ca 
Filled with Copper 
Gauze 




Fig. 74. — Ellison's Steam Calorimeter. 



Fig. 75. — Thomas' Electric Steam 
Calorimeter. 



Steam enters at the bottom of the vessel at A and passing upward 
through the heated coils the moisture contained in it is evaporated. The 
steam then passes up through a perforated casing filled with copper 
gauze and escapes through the pipe discharging at the side at C. A part 
of this latter pipe is made of a glass tube for observing the condition of 
the steam. A thermometer is inserted at T for observing the tempera- 
ture after this reheating. 

In the operation of the instrument a steady flow of steam must first 
be secured, then the electric current should be turned on to dry the steam. 

1 If the calorimeter is not exceptionally well lagged with a steam jacket or with 
heavy heat-insulating material, a correction for radiation is necessary, as explained 
for a separating calorimeter on page 64. 



70 POWER PLANT TESTING 

When it is dry or superheated the fog will disappear from the glass 
observation tube. The first step is to superheat the steam to some 
temperature T, requiring an electrical input of B* watts. Then decrease 
the current until the steam is just dry, requiring an input of E watts. 
Then E t — E = E' which represents the watts required to superheat 
the steam t degrees to the temperature T. By applying a constant 
K, determined by experiments, for a series of pressures and degrees of 
superheat, the following equation is obtained: 



. KE 



where h is the heat (B.t.u.) required to dry a pound of steam. A series 
of curves giving values of K are supplied with each instrument. If r 
is the heat of vaporization of the steam corresponding to the pressure 
then the quality 

r-h . . 

x = — — (4a) 

Although this apparatus is used for steam of high quality as well as 
low, it has not been generally used probably because throttling calorim- 
eters are preferred on account of greater simplicity in both construction 
and operation, and because very often a source of electric current is not 
conveniently available where tests are to be made. No data are avail- 
able comparing its efficiency with that of the combined separating and 
throttling calorimeters described in the preceding paragraphs, but for 
accurate tests the latter are generally preferred by engineers. 

Errors in this type of instrument are likely to be due to a variable 
weight of steam discharging in a unit of time; that is, the weight dis- 
charged will be less for. superheated than for dry saturated steam. If, 
however, the steam discharged is condensed and weighed, the error from 
this source can be eliminated. It is practically impossible to make 
enough curves of values of K for all the variables. 

Barrel Calorimeters. There is still another kind of steam calorimeter, 
known as the Hoadley barrel type, deserving some attention. It is one 
of the oldest forms of apparatus for making determinations of the quality 
of steam. In the classification made at the beginning of this chapter 
it belongs in the group of condensing calorimeters. Even with expert 
manipulations, ordinarily it is much less accurate than any of the calorim- 
eters already described. A typical apparatus of this kind is shown in 
Fig. 76. It consists usually of a weighing barrel B, made of three con- 
centric vessels of galvanized iron with the two annular spaces between 
the inner and outer vessels filled with pressed sheet cork or hair felt to 
reduce radiation to a minimum. It is usually arranged so that when 
the inner vessel has been nearly filled with water from the barrel A, a 



DETERMINATION OF THE MOISTURE IN STEAM 71 




Barrel" Steam 
rimeter. 



quantity of the steam to be tested can be passed into it. The steam is 

admitted into the barrel in the most common forms by disconnecting the 

water hose R at C and making a temporary connection from the steam 

pipe out of which a sample is to be 

taken to a vertical pipe in the barrel 

of sufficient length to extend nearly to 

the bottom of the inner vessel. The 

pipe may be plugged at the lower end 

and sufficient area for the escape of 

steam is then secured by drilling into 

the pipe a number of |-inch holes for 

some distance from the lower end. 

This arrangement will make it easier 

to secure an equal rise in temperature 

in the different parts of the barrel. A 

float is usually provided to show the 

depth of water in the barrel, and a 

suitable stirring device or agitator consisting of paddles attached to a 

vertical shaft is also needed. This agitator when revolved stirs up the 

water and brings it to a constant temperature. 

Briefly the method to be pursued in the operation of the barrel cal- 
orimeter may be outlined as follows: First fill the barrel with cold water 
until the float shows that the water level is about six inches from the 
top. Then stir well, observe the temperature accurately and weigh 
carefully on a platform scales. The steam pipe should then be connected 
up to discharge into the water after first allowing the steam to blow off 
into the air, for the purpose not only of removing the condensation in 
the piping, but also to heat it to as nearly as possible the temperature 
of the steam. When the temperature has risen to about 120 degrees 
Fahrenheit the steam should be shut off and another weighing made to 
determine the amount of steam added. While the weighing is being 
done the water should be stirred vigorously and the highest temperature 
observed. For all the weighings the piping must be in exactly the same 
position as regards the connection on the barrel and all the pressure in 
the pipes must be relieved. When the piping between the calorimeter 
and the steam supply is connected by pipe fitters' unions these should 
be disconnected to insure the best accuracy. When, however, the con- 
nection is made by means of flexible rubber hose the weight can probably 
be obtained accurately enough without disconnecting the piping if the 
precaution is taken to relieve the pressure in the piping by opening a 
petcock located in the steam pipe near the point where it enters the 
barrel. 

If, just before making the test for the quality of the steam, the cal- 



72 POWER PLANT TESTING 

orimeter is filled with water, heated with steam or otherwise to about 
150 degrees Fahrenheit and again carefully drained, the barrel will be 
near its average temperature during the test, and no correction need 
probably be made for the heat absorbed by the calorimeter. In most 
cases it is preferable, however, to determine accurately the heat absorbed 
by the calorimeter and then make the proper corrections; but unless 
the work be done very carefully it is valueless. This correction is usually 
made by calculating the water equivalent or the capacity of the calorim- 
eter to absorb heat measured by the similar capacity of water. The 
water equivalent is to be added to the weight of water in the calorimeter. 
Using then the following symbols: 

w' = weight of water in calorimeter, in lbs. 

w" = weight of water added, in lbs. 

t' = temperature of water in calorimeter, deg. Fahr. 

t" = temperature of water added, deg. Fahr. 

t'" = temperature of mixture, deg. Fahr. 

k = water equivalent, in lbs. Then 

(w' + k) (t'" - 1/) =w"(t"-t'"), 

w" (t" - t"0 , , , 

k = — t'" - t' (5) 

The temperature of the water added should be taken just as it enters 
the calorimeter and as near to it as possible. 

The quality of the steam (x ) to be determined is calculated as follows: 

Wi = weight of water in calorimeter, in lbs. 

W2 = weight of steam added, in lbs. 

k = water equivalent of calorimeter, in lbs. 

ti = initial temperature of water in calorimeter, deg. Fahr. 

t 2 = final temperature of water, deg. Fahr. 

p = pressure of steam, lbs. per sq. in. 

r = heat of vaporization of steam (B.t.u.) corresponding to po. 

q and q 2 = sensible heat of steam (B.t.u.) corresponding to p and t 2 . 

Then equating the heat lost by the steam to the heat gained by the 
water, 1 

(xoTo + qo - q 2 ) w 2 = (wi + k) (t 2 - ti) ... (6) 

(wi + k) (t 2 - ti) q 2 - qo , , 

xo = — 1 (7) 

w 2 r r 

1 Equation (7) can be made a little simpler for calculations without appreciable 
error by writing for (q 2 — qo) the difference between the corresponding temperatures 
(ti -to). 



DETERMINATION OF THE MOISTURE IN STEAM 73 

The accuracy of this instrument depends principally on the care with 
which the various temperatures and the weight of the condensed steam 
are obtained. Usually it is very difficult to obtain accurately the 
temperature of the mixtures of water and steam. It is not unusual 
for determinations of moisture with such a calorimeter to vary for the 
same quality of steam and with expert handling as much as 5 per cent. 
In the case, therefore, of steam with 10 per cent moisture, the determi- 
nation of quality might be in error as much as one-half per cent. 

Calorimeter Calibrations. For a laboratory calibration exercise three 
calorimeters of different types are connected by means of exactly the 
same kind of fittings and valves to the same steam main or receiver. A 
water-jacket or a device like that shown in Fig. 44 should be provided 
to vary the quality of the steam. Tests should be made simultaneously 
and for the same length of time on the three instruments. 

Relative Accuracy of Calorimeters. Because of greater accuracy, 
comparatively small size, portability, and general indestructibility, 
throttling calorimeters are generally preferred by engineers. In the 
order of their relative accuracy steam calorimeters are usually classed 
as follows: (1) throttling; (2) combined separating and throttling; (3) 
separating; (4) electric; (5) barrel. 



CHAPTER IV 

MEASUREMENT OF AREAS 

Two methods are in general use for obtaining the area of irregular 
figures like indicator diagrams: (1) by measuring ordinates; and (2) 
by means of a planimeter. Variations of the method of ordinates are 
known as trapezoidal, Durand's and Simpson's. To find the area by 
any of these methods divide the figure into an even number of strips by 
parallel lines. The accuracy is increased as the number of strips is 
made larger. The notation used in the formulas is illustrated in Fig. 78, 




Fig. 78. — Diagram of Ordinate 
Methods. 




Fig. 



- Gramberg's " Line 
Pattern." 



where y is the length of the first ordinate, yi of the second, etc., n is the 
number of strips, w is the common width of the strips and A is the area 
of the figure. Then the following approximate formulas may be stated: 



I. By trapezoidal rule, 

A = u> (! y + Vi + 2/2 + 

II. By Durand's rule, 

A = w (0.4 y + 1.1 y x + y 2 + y 3 + • 

III. By Simpson's rule, 

A = \w {y n + 4 2/1 + 2 y 2 4- 4 y 3 + 



+ yn-i + $y n ). 



+ y n - 2 + l.li/„_x + 0.4j/ B ). 



+ 2y B _ 2 + 4y n -i+.j/n). 



A very convenient method of measuring areas by the use of a " line 
pattern " has been devised by Granberg. 1 A sheet of tracing cloth or 
thin celluloid is prepared with parallel lines on it, equally spaced, and 
with dotted lines (Fig. 79) as shown, located at each end of the figure 
at one-fourth the distance between the unbroken lines first drawn. This 
" line pattern " is then laid upon the area to be measured so that the 

1 Granberg, Technische Messungen, page 48. 
74 



MEASUREMENT OF AREAS 75 

ends of the area fall on the " solid " parallel lines at opposite ends. The 
sum of the lengths of the " solid " lines included by the outline of the 
area added to one-half the sum of the lengths of the two dotted lines 
included at the ends when multiplied by the distance between the 
parallel " solid " lines (b) gives the required area. 

The various lengths required for both Granberg's and the trapezoidal 
rules can be conveniently added by laying them off with a dividers one 
after the other along a straight line and finally measuring the total length 
of the line. 

Areas are also frequently calculated by the method of mean ordinates, 
as given on page 142, for finding the mean effective pressure in engine 
cylinders. 

Planimeters. The most accurate and generally approved method 
of obtaining the area of irregular figures is by means of integrating in- 
struments called planimeters. Instruments of this kind may differ in 
many details, yet all of them are based, in theory, on the original Amsler 
polar planimeter. 

Polar Planimeters. One of the simplest forms of the polar type of 
planimeters is shown in Fig. 80. It consists essentially of two arms PO 
and TO pivoted together at O. When in use the point P is not to be 
moved, and is held in place by means of a pin-point upon which a small 
weight rests. There is a tracing point at T intended to be moved around 
the border of the area to be measured. Attached to the arm TO is a 
small graduated wheel W carried on a short axis which must be placed 
accurately parallel to TO. Any movement of the arm TO except in the 
direction of its axis will, of course, move the wheel W on the paper or 
other surface on which it is placed in such a way that the amount of its 
movement gives a record indicating the area measured. A vernier V placed 
opposite the graduations on the wheel, assists in reading the instrument 
accurately. The arm TO is usually made of such a length that the move- 
ment of the tracing point T around an area of one square inch (for English 
units) will move the wheel one-tenth of its circumference. Graduations 
of the vernier indicate usually one one-thousandth of a revolution of the 
wheel, or in English units one one-hundredth of a square inch. 

When the tracing point T is moved around an area in a clockwise 
direction the wheel will roll in the direction of its graduation, and the 
area is found by subtracting the final reading from the initial. Amsler 
planimeters are often constructed with the arm TO adjustable in length, 
so that it can be set to indicate areas in various units, as, for example, 
square inches, square feet, square centimeters, etc. 

The vernier V has ten graduations, and the total length of these ten 
divisions is one-tenth less than the length of those on the wheel so that 
it represents, counted from zero, so many hundredths of a square inch. 



76 



POWER PLANT TESTING 



To explain the method of using the vernier, Fig. 81 has been inserted, 
showing the wheel W and the vernier V in a drawing of larger scale than 
in Fig. 80. Readings of the graduations on the wheel W are always 
taken opposite the zero mark on the vernier, so that the reading indicated 




Fig. 80. — Amsler Polar Planimeter. 



in Fig. 81 without the help of the vernier would be a little more than 4.7. 
The graduation on the vernier which is exactly coincident with a gradu- 
ation on the roller wheel is the third from zero and indicates three 
hundredths. The complete reading is therefore 4.73 as determined by 
the vernier. 



^1- 



1 




Fig. 81. — Typical Vernier for 
Planimeter. 



P w 

Fig. 82. — Position of the Arms of a Polar 
Planimeter to Draw the "Zero" Circle. 



Theory of Polar Planimeters. As this instrument is constructed 
neither of the points T nor W can pass over the arm PO (Fig. 82). If 
the arms PO and TO are clamped so that the plane of the graduated 
wheel W intersects the point P, x that is, when the'angle TWP is a right 
angle, and then the arms thus clamped are revolved around this point, 
the wheel will be continually slipping without any rolling motion in the 

1 As regards the theory it is immaterial whether W is between O and T or on TO 
extended. Some planimeters are made one way and some the other. 



MEASUREMENT OF AREAS 



77 



direction of its axis, and consequently it will not revolve. When, how- 
ever, the arms are not clamped and if the construction of the instrument 
will permit the tracing-point T to be moved out so far that the axis of W 
will lie in the line PO, then an arc described by the movement of T will 
produce only a rolling motion of the wheel. Obviously with the arms in 
any position intermediate between that of the clamped right angle and 
the one with W in line with PO, the wheel will partly slip and partly roll, 
the amount of slipping and rolling depending on the size of the angle 
between the arms. It follows, then, that when circumscribing a closed 
figure the radial components cause 
only slipping of the wheel and need 
not be considered, while the circumfer- 
ential components produce a resultant 
rolling which must be taken into con- 
sideration. 

The path described by the tracing 
point T when the arms are clamped, 
as indicated in Fig. 82, is called the 
zero-circle for the planimeter. If the 
tracing-point is moved in any path 
outside the zero-circle in a clockwise 
direction a positive record will be 
indicated on the graduated wheel, 
while if it is moved in a path in the 
same direction as before but inside 
the zero-circle there will be a negative 
record. 

According to the theory of polar planimeters, they are designed so 
that the rolling of the wheel for a given circumferential motion of the 
tracing-point T is proportional to the area included between the path of 
T, the radial lines from P (Fig. 83) to the initial and final points of the 
path taken by T, and the arc of the zero-circle included between these 
radial lines. In other words, the area referred to is QTT'Q' in Fig. 83. 
In the discussion of this theory, the circumferential motion of the tracing- 
point T around the point P, with the angle WOP (marked a) remaining 
always at a constant value, is to be taken up first. 1 Now let us suppose 
the tracing-point is moved from T to T' in the figure through a very 
small angle, TPT' (marked e), keeping, however, the angle a constant; 
then the graduated wheel W will move through the arc WW', partly 
rolling and partly slipping. The component of this motion producing 




Fig 



■ Theoretical Diagram for a 
Polar Planimeter. 



1 In the mathematical discussion following, the graduated wheel will be considered 
as if it were a part of the arm TO, with its plane exactly at right angles to the axis of 
this arm. 



78 POWER PLANT TESTING 

rolling will be perpendicular to the axis of the wheel; or, in other words, 
this component will be perpendicular to OT in all its positions, and 
without appreciable error for small values it may be represented in 
this figure by the line WX, making WXW a right-angled triangle of 
infinitesimal proportions. When the tracing-point has moved from T 
to T' the point O has moved through the arc 00' and the tracing-point 
subtends in its movement an angle WPW, which is equal to the angle 
TPT', marked e, which was passed over by T. Then the following 
relation is easily obtained: 

WW' = PW X c. 

In this equation the symbol c is a constant, expressing the ratio (for a 
given angle WPW) of the length of an arc to the corresponding radius for 
any value of this radius. In other words, in terms of the calculus this 
constant would be expressed in radians. In general for every angle there 
is a constant value which when multiplied by the radius gives the length 
of the arc for that radius. 

The component of WW' corresponding to the rolling of the wheel is WX, 
which is approximately equal to the arc WW times cos WWX. That is, 

WX = PW X c X cos WWX (8) 

But if PY is drawn perpendicular to T'W produced 

PW cos WWX = WY, (9) 

and combining (8) and (9), 

W'Y = ^ (10) 

c ' v 

Since the angle WPW is very small, WW may be taken as being per- 
pendicular to WP. Now WX is perpendicular to T'Y and the angle 
WWX is equal to the angle PWY. The trigonometric relations reducing 
the above to terms of the length of one of the arms of the planimeter and 
the constant angle a are as follows: 

WY 
W'Y = ^^ = PW'cosPWY = PO / cosPO'Y-WO' = PO / cosa-WO / , 
c 

then WX = c (PC cos a- WO') (11) 

This is an expression for the amount of rolling of the wheel when the 
tracing-point moves from T to T'. 

To express the relations required, the area will now be expressed 
trigonometrically in similar units. From geometry the area of sector 
TPT' = 1/2 arc TT' X PT, but arc TT' = PT X c, or area TPT' = 
1/2 c X PT 2 . 



MEASUREMENT OF AREAS 79 

We can write also, 

PT = VpQ 2 + OT 2 + 2 PO X OT cos a, 
area TPT' = 1/2 c (PO 2 + OT 2 -f- 2 PO X OT cos a). . (12) 

But the area represented by the amount of rolling of the graduated wheel 
is that part of the sector outside the zero-circle (see page 77), and this is 
the area TT'Q'Q. Now the radius r of the zero-circle, referring again 
to Fig. 82 ,* is easily obtained from equations expressing the relations of 
the sides of the right triangles in that figure for the particular case when 
there can be no rolling movement. Thus, 

PO 2 = WO 2 + PW 2 , (13) 

PW 2 = PT 2 - WT 2 = PT 2 - WO 2 - 2 WO X OT - OT 2 . . (14) 

Combining equations (13) and (14), 

PO 2 = WO 2 + PT 2 - WO 2 - 2 WO X OT - OT 2 . 

But PT = r, the radius of zero-circle, therefore, 

r = VpO 2 + 2 WO X OT + OT 2 . .... (15) 
Also from geometry, as explained on the preceding page, 
Area QPQ' - 1/2 r X c X r = 1/2 c X r 2 

= i/2c(P0 2 + 2WO XOT + OT 2 ) (16) 

Subtracting equation (16) from equation (12), 

Area QTTQ' = c X OT (PO cos a - WO). . . . (17) 

Equation (17), which is the expression for the area outside the zero- 
circle, will be observed to be equivalent to the roll of the graduated wheel 
as given in equation (11), times the length of the arm OT from the pivot 
to the tracing-point. If, therefore, for a given area A, we call the reading 
of the wheel R and the length of the arm from pivot to tracing-point L, 
then, 

A = LR . (18) 

It should be noted further that this equation is independent of any 
other dimensions of the instrument. 

That this demonstration applies to areas not adjacent to the zero- 
circle or partly inside and out can be readily shown by subtracting in a 
given case the area between the zero-circle and the required area. 

1 It will be remembered that with the arms of the planimeter in the position shown 
in Fig. 82 the tracing-point T describes the circumference of the zero-circle. 



80 POWER PLANT TESTING 

Area of Zero-Circle by Experiment. The area of the zero-circle of a 
planimeter may be found readily by passing the tracing-point around 
the circumference of two circles each larger than the zero-circle. Pref- 
erably for this operation the fixed point of the instrument is placed 
at the center of the circles. If the calculated areas of these circles are 
respectively Ai and A 2 , and r is the radius of the zero-circle, then since 
readings of the graduated wheel show only the areas outside the zero- 
circle represented by Ri and R2, we obtain 

Ai = xr 2 + Ri, 
A 2 = Trr 2 + R 2 , 
2 Trr 2 = Ai + A 2 - (Ri + R 2 ) (19) 

After r has been found 1 it is not difficult to calculate the proper length 
of the arm OT for any linear units (compare equation 15). In fact very 
many polar planimeters are constructed with the arm OT adjustable, so 
that the instrument can be used for any scale or for various units. The 
exact lengths required for both the English and metric units (inches and 
centimeters) are usually stamped on the adjustable arm. 

Mean Ordinate of an Area. 2 If we call m the mean ordinate and 1 
the length of a given area A, then 

A = ml. 

From equation (18) we have 

A = LR, 
whence 

ml = LR, 

m = y R (20) 

1 If instead of measuring and calculating the circles both larger than the zero-circle, 
one of the two is made smaller than the zero-circle, then the reading of the instrument 
is again the difference between the area of the circle and that of the zero-circle, but the 
value of this difference is now negative, so that if Ai is the area of the circle larger than 
the zero-circle and A 2 is the area of the one smaller, then using the other symbols as 
before, 

Ai = xr 2 + Ri, 
A 2 = Trr 2 - R 2 , 
2 Trr 2 = Ai + A 2 - (Ri - R 2 ). 

Although this latter method does not fall in with the general demonstration so well, 
it is, however, usually preferred, as it will give greater accuracy than can be obtained 
with two circles both larger than the zero-circle, unless one of these is made unusually 
large. 

2 Engineers must calculate mean ordinates most often when determining the mean 
effective pressure (m.e.p.) of engine indicator diagrams. 



MEASUREMENT OF AREAS 



81 



When, therefore, the tracing-point arm is adjustable it may be set as 
shown in Fig. 84 1 to make it equal to the length of the area measured. 
Then, obviously, the height of the mean ordinate will be equal to the 
reading of the graduated wheel expressed in the same units. For ex- 
ample, if the subdivisions of the wheel are fortieths of an inch, the result 
will be the mean ordinate also in fortieths. This scale of the wheel is 
not determined by the diameter of the portion of the wheel which is 
graduated, but by the diameter of the edge which comes into contact 




Fig. 84. — Polar Planimeter with Adjustable Arms for the Rapid Determination of 
Mean Ordinates. 

with the surface over which the wheel rolls. If then d is the so-called 
diameter of " rolling " of the wheel, its circumference is xd. Now by 
dividing the number of divisions on the circumference (usually 100) 
by 7rd, the "scale" of the wheel is obtained. It may also be found by 
measuring a rectangular area of the same length as that of the tracer 
arm and one inch wide, when the reading from the wheel will give the 
number of divisions per inch. For those instruments of which the radius 
of the wheel is one centimeter (.795 inch diameter) and having 100 
divisions, the scale is almost exactly 40 divisions to the inch. 

Coffin Planimeter and Averaging Instrument. This planimeter is 
made commonly in two forms, illustrated by Figs. 85 and 86. As re- 
gards details the former is somewhat the simpler and will be explained 
first. In principle the two are exactly alike. As will be observed in the 
figures, this instrument has a single arm to which a suitably graduated 



1 To facilitate the adjustment of the arm to the length of the diagram or area meas- 
ured, sharp points M and N are attached to the back of some planimeters. The point 
M is often conveniently placed a short distance away from the tracing-point T, and 
the point N must then be the same distance and in the same direction away from the 
pivot O. Then obviously the distance between M and N will be in all cases equal to 
the length of the adjustable arm. 



82 



POWER PLANT TESTING 



wheel is attached on an axis parallel to the line joining the ends of the 
arm. One of the ends of this arm is for tracing the outline of the area 
measured while the other slides up and down in a suitable slot. One of 
the advantages of this instrument over the polar planimeter, although 
it is not so generally adaptable, is that the wheel is made to move over 
a specially prepared surface, preventing unnecessary slipping. On mate- 



c-f 



: 






WSj/p* warn 



Fig. 85. — Coffin Planimeter. 




3. — Coffin- Ashcroft Averaging 
Planimeter. 



rials having a rough, fibrous or, worst of all, an uneven surface, the 
movement of the wheel of any planimeter will not be the same as when 
rolling over a smooth flat surface. 

The Coffin planimeter may be discussed as a special form of the general 
polar type in which the pivoting point O, instead of swinging about the 
fixed point P (Fig. 8o), moves back and forth in a straight line. The 
angle between the arms PO and OT, as indicated by the dotted lines in 
Fig. 87, is really invariable at 90 degrees. Obviously, then, the equation 
(17) expressing the area traced by a polar planimeter outside the zero- 
circle becomes, referring to Fig. 83, 

area = c X OT(- WO); 

likewise equation (11), expressing the roll of the wheel for the Coffin 
planimeter, becomes equivalent to 

Roll or record of the wheel = c (- WO') = c (- WO). 

Using, as before, in equation (18), the symbols L and R for, respec- 
tively, the length of the arm OT and the reading of the wheel, we have, 
just as for the polar planimeter, 

A = LR (21) 



MEASUREMENT OF AREAS 



83 



As an averaging instrument the Coffin planimeter is very much more 
convenient than the typical forms of polar planimeters. For finding 
the mean ordinate of an area the use of the polar type of these instru- 
ments was explained on page 80. The sliding vertical straight edge 
shown at the right in Figs. 85 and 86 is for the purpose of making the 
operation of finding the mean ordinate of an area (or the " mean effec- 
tive pressure " of an engine indicator diagram) as simple as possible. 



P \ 



V 




Fig. 



Theoretical Diagram for a Coffin Planimeter. 



For this operation the straight edges C and K should be adjusted so that 
when the tracing pin passes over the extreme end of the area to be 
measured it will just touch both of them. Now if the tracer is started 
at either end of the area and moved around to the starting point and 
then moved upward along the vertical straight edge until the reading 
of the wheel is the same as when starting to trace the area, this last 
distance traced from the starting point along the vertical straight edge 
is the mean ordinate. To demonstrate this statement the symbols used 
on page 80 will be continued. Representing the mean ordinate by m, 
the length of the area A by 1, the reading or rolling of the graduated 
wheel in going around the area by R, and the length of the arm carrying 
the tracer by L, then as before 

A = ml. 



Now, when the tracing-point T moves over a vertical line, the angle 
DOT, represented by Z in Fig. 88, remains constant. If we call the 
vertical distance moved V, and remember that only the movement of 
the wheel at right angles to its axis produces rolling, then the reading 
corresponding to the rolling R is 



R = VsinZ. 



(22) 



84 



POWER PLANT TESTING 



But for the position shown in Fig. 87 when the tracer T is at the right- 
hand end of the outline of the area, we have 

1 



sinZ 



whence 



VI 
L 



Substituting this value of R in the general equation (20) for the mean 
ordinate m of a polar planimeter, then, 

LV1 XT < \ 

m= TT (23) 

This relation can be illustrated more simply, however, by referring to 
Fig. 89, which is a typical indicator diagram from a steam engine. In 





Fig. 88. — Theoretical Diagram for a 
Coffin Planimeter. 



V, 

Fig. 89. — Diagram Explaining the Method 
of Mean Ordinates with a Coffin Planimeter. 



this figure the tracing-point of the Coffin instrument is shown at O, with 
the tracing arm represented by VO. A rectangle OXYZ, indicated by 
dotted lines, is shown, of which the area is equal to that of the indicator 
diagram. Starting at O and moving the tracing-point around the in- 
dicator diagram once, the difference in readings is the area. Now if 
the tracing-point is moved in the opposite direction around the rectangle 
and again back to the starting-point at O it will measure a negative 
area equal to the first area and the reading of the graduated wheel will 
be the same as when first started around the indicator diagram. The 



MEASUREMENT OF AREAS 



85 



movement of the graduated wheel as the tracing-point moves from X 
to Y is equal and opposite to that in going from Z to O, so that these 
two cancel each other. The motion of the tracing-point from Y to Z 
requires the axis of the graduated wheel to be parallel to YV and con- 
sequently during this movement the wheel will not be moved. The 
only movement that is therefore producing a net change in reading of 
graduated wheel during the reverse tracing of the rectangle is in going 
from O to X. Consequently after going around any irregular area like 
an indicator diagram in a clockwise direction from the starting-point at 
O at the right-hand end of diagram, if the tracing-point is moved in a 
vertical direction from the starting-point at O until the reading of the 
graduated wheel is the same as when first started, this vertical distance 
moved, measured from O, will be equal to the mean height of the indi- 
cator diagram. 





— ^=^^\ 




\vx 


"lllllll 

R 2 


\ 


3 






l-= 






Fig. 90. — A Typical Roller Planimeter. 



Although measurements of areas may be made with the Coffin planim- 
eter as with the regular polar types with the area in any position as 
regards its length and breadth, yet when the mean ordinate is to be 
obtained, its value in a definite position is required and the area must 
be placed so that its length with respect to which the mean ordinate is 
to be obtained will lie along the horizontal straight edge shown in the 
figures. Then the mean ordinate measured along a vertical straight 
edge will give the result required. 

Roller Planimeters. For the measuring of very large areas a planim- 
eter differing slightly in theory from the polar type has been designed 
by G. Coradi, of Zurich, Switzerland. It has the advantage of being 
adaptable for measuring surfaces of indefinite length and as wide as the 
length of the tracer arm. This instrument is illustrated in Fig. 90* 



86 POWER PLANT TESTING 

It is supported at three points — the two rollers R 1 and R 2 and the trac- 
ing pin f, or its support s. These two rollers are attached to the shaft A. 
On the face of one of these rollers is a minutely divided miter-wheel 
engaging with a small pinion revolving the horizontal shaft carrying 
the spherical segment K. At the center of the frame B, and in the 
same vertical plane with the two shafts already mentioned, a vertical 
shaft carrying the tracer arm is supported. The spherical segment K 
causes merely by friction contact the movement of the cylindrical 
"measuring" roller shown at its right. This roller is supported on 
the auxiliary frame M, of which the tracer arm is a part. The " meas- 
uring" roller moves back and forth with respect to the spherical seg- 
ment to correspond with the movement of the tracing-point; but at the 
same time the rotation of the segment itself imparts rolling motion of 
the entire instrument. 1 

Calibration of Planimeters. Tests are made by comparing the read- 
ings of the instrument with that calculated for a given area. For such 
calibrations it is necessary to use an area which can be gone over accu- 
rately with the tracing-point preferably held mechanically. This is done 
usually by using a metallic testing rule, shown in Fig. 91. It is usually 



1 ' I 1 1 



# 



Fig. 91. — Planimeter Testing Rule. 

made in the shape of a narrow strip from three to five inches long. At 
the end marked zero on the graduations a needle point is set which is 
kept in place by an overlapping screw. At each line of the graduations 
there is a very small conical hole into which the tracing-point of the pla- 
nimeter can be placed. The beveled end of the testing rule has the index 
line set accurately at the starting mark, so that this point can be very 
carefully located. With the tracing-point T in the testing rule and the 
fixed point P of the planimeter in approximately the position shown in 
Fig. 92, observe the reading of the instrument corresponding to the area 
of the circle described by the tracer moving clockwise, in the positions 
shown. 

1st. When the fixed point P is on the left-hand side of the tracing 
point. 

2d. When P is on the right-hand side. 

1 Since this instrument is not often used by engineers, those interested in its theory 
are referred to Coradi's book of directions (in English) accompanying each instrument, 
or to Handbuch der Vermessungskunde, by W. Caville. 




MEASUREMENT OF AREAS 87 

If the reading obtained is greater in tne first position than in the 
second, the end of the shaft carrying the graduated wheel nearest the 
tracing-point must be shifted toward the right to make the instrument 
accurate, and vice versa. Otherwise the error, if there be one, can be 
eliminated by taking the mean of the results obtained for the two 
positions. 1 

Another test to be made, if there is doubt about the accuracy of a 
planimeter after the axis of the wheel has been adjusted, is to determine 
whether the settings of the adjustable arm marked on the instrument 
are correct. For this determination 
circles with several different diameters 
can be measured with the testing 
rule, and if there is a nearly constant \ 
percentage error, say x per cent too 
large, then the adjustable arm must 
be lengthened x per cent to make the 
planimeter readings correct, and vice 
versa. 

For accurate results the fixed point 
P should be placed as indicated by ^ 92 _ Me ^ ds "" f Testing 

the dotted lines in Fig. 92, so that Planimeters. 

when the tracing-point is near the 

center of the area to be measured the two arms will be approximately at 
right angles. 

Durand-Bristol Integrating Instrument. This instrument, illustrated 
in Fig. 93, has been recently developed by the Bristol Company for ob- 
taining the average radius of records traced on circular charts of uniform 
graduations like those used in recording gages, thermometers, etc. It 
is a simple device for obtaining quickly the average value of pressure, 
temperature, draft, watts, volts, amperes and other records generally 
taken on circular charts. 

This instrument consists of a wooden base in which there is a metal 
socket for supporting a rotatable pin slotted for receiving a horizontal 
shaft to which the integrating wheel is rigidly attached. On this shaft 
between the integrating wheel and the pin there is an adjustable tracing- 
point and at the opposite end of the shaft there is a triangular support 
for the shaft, also adjustable. 

The general principle of this instrument is due to Professor W. F. 

1 For ordinary requirements a testing disk can be used in place of the rule, although 
it is not usually so accurate. On this disk circles of 1, 2, and 2| inches diameter are 
usually engraved; and if neither a testing plate nor a disk is available, tests can be 
made by using circles drawn with a pencil compass on a flat sheet of well-calendered 
paper. 



88 POWER PLANT TESTING 

Durand 1 of Leland Stanford University. Its application hinges on the 
condition that the chart to be measured has a uniform radial scale, the 




Fig. 93. — Bristol-Durand Integrating Instrument for Circular Charts. 

same as there must be a uniform vertical scale for indicator and other 
similar diagrams in order that they can be averaged with the ordinary 
planimeters. Obviously the mean value of the radius of a circular 




Fig. 94. — Diagrammatic Drawing of Bristol-Durand Integrating Instrument. 



diagram cannot be determined with ordinary planimeters, since the area 
of a diagram in polar co-ordinates is proportional to the square of the 

1 Transactions American Society of Mechanical Engineers, vol. 29 (1908). 



MEASUREMENT OF AREAS 89 

radius and to the angle. 1 In Fig. 94 AB is an irregular curve, considered 
for this theoretical discussion as traced by a point moving in and out on 
a straight radial line. The center of the chart is at O, and at this point 
there is a socket, in which a rod O'P slides freely back and forth, permit- 
ting a tracing-point P to draw a curve AB. A graduated wheel W 
attached to O'P serves the same general purpose as the integrating wheel 
in the ordinary planimeter. Obviously this wheel will be moved only by 
circumferential motion, and for any radial movement of the rod in the 
direction of its length it will remain stationary. The amount of move- 
ment will be proportional to the radius WO, which differs from PO by 
a constant distance PW. The resultant movement of the wheel W is 
proportional, therefore, to the angle moved by the arm O'P and to the 
radius OW varying from point to point along the curve. Assuming for 
the present, but as will be shown later, the reading for any part of the 
curve, as AB, to be proportional to the product of the angle subtended 
between the points A and B, AOB, and the mean radius for the curve 
between these points, then if this reading is divided by the subtended 
angle expressed in circular measure the quotient will be proportional to 
the mean radius. Now if to the value of this mean radius the constant 
distance WP is added, the true value of the radial ordinate OP is ob- 
tained. When, as is usually the case in practice, the curve AB repre- 
sents values of radial ordinates with reference to a base circle of constant 
radius as the datum or " zero line," then if the radius of this base circle 
is subtracted from OP the remainder will be the true value of the ordi- 
nate. By making WP equal to the radius of the base circle, as may 
readily be done by a suitable adjustment of the instrument, the two 
corrections will be " balanced " and the mean value of the radial ordi- 
nate will be given directly as the quotient of the reading of the wheel 
and the subtended angle AOB expressed in circular measure. For a 
chart corresponding to twenty-four hours for a circumference, the angular 
measure to be used as the divisor will be .2618 per hour. 

The quantity to be determined in such diagrams is the time-mean 
of the quantity measured by theradialordinate. But since angular 
motion is made proportional to time, we may represent the desired mean 
by the following integral formula: 






rd0 

(24) 



Now, in Fig. 95, let ABCD denote a curve drawn by a tracing-point 

1 With the ordinary planimeter the mean square of the radial ordinates can be 
determined, and we can, of course, take the square root of these values, but in most 
cases this is not the same as the mean radius. 



90 



POWER PLANT TESTING 




value 



rdfl. 



which moves on the arc of a curve shown by OAV instead of on a straight 
radial line. Then let OV, ON, OM, etc., denote a series of consecutive 
positions of the curve OAV, at differential angular intervals 6.6. Then 
for the actual curved path ABCD substitute the broken line path made 
up of a series of arcs each rd0 in length, and the series of differential bits 
of the curve OAV as shown. Then at the limit the record of any inte- 
grating or averaging instrument will be the same, whether the tracing 
point is carried along the curve or along the broken line as shown. 

Then suppose an integrating instru- 
ment, as shown in Figs. 93 and 94, is 
applied to such a diagram, and let the 
tracing-point P be carried along the 
zig-zag path. The record of the wheel 
will be made up of two parts: 

1. That due to the circular arcs rd# 
and representing by summation the 

of/r 

2. That due to the differential por- 
tions of the arc OAV. 

Now it is clear that if the diagram 
extends all the way around from A 
through BCD to A again the differential 
elements of the curve OAV may be considered as existing in pairs, and 
that for every element traversed in the outward direction there will be 
an equal element traversed in the inward direction. PQ and ST denote 
the members of such a pair. The record for such a pair will therefore 
disappear in the summation; that is, for all the pairs, and also for the 
diagram as a whole. In such a case, therefore, part " 2 " above be- 
comes zero and the record of the wheel for the entire diagram consists 

simply of / rd0. 

This reasoning is seen to be entirely general and independent of the 
character of the path OAV, and hence must be true whether it be the 
arc of a circle, a straight line or any other path. • 

In case the curve occupies only part of the revolution, as ABC, then it 
is clear that in going from A to C the record will involve the two parts, 
" 1 " and " 2 " above, and that the latter will remain included in the 
final result and will represent the summation of the record due to the 
elements of OAV between A and C. This obviously will be the value of 

/ rd(9 for the arc GC and it will be canceled by carrying the tracing-point 

of the instrument back from C to G. This method of reasoning is inde- 



Fig. 95. — Theoretical Curves for 
Bristol-Durand Instrument. 



MEASUREMENT OF AREAS 91 

pendent of the extent of the arc and is therefore equally true for an entire 
revolution, even when the diagram does not end at the same radial dis- 
tance, as at the beginning. In such cases it is necessary only to trace 
along the arc OAV so as to " close " the curve, thus canceling part " 2 " 

above and finding directly the value of / rd0 for a whole revolution. 

In all cases the correction for part " 2 " of the record is made by tracing 
from the terminal point of the curve along the path, representing no 
change of time to a point lying in a circumference passing through the 
initial point. This may be stated in other words by saying that to 
eliminate part " 2 " of the record the tracing-point must start and finish 
at the same distance from the center, and if the diagram is not of the 
kind to satisfy this condition then the necessary portion of a path of zero 
change of time must be used to supplement- the diagram. This discus- 
sion is independent also of the nature of the curve OAV. It may be 
stated, however, that when OAV becomes a straight line the value of the 
correction becomes zero. 



CHAPTER V 

ENGINE INDICATORS AND REDUCING MOTIONS 

The engine indicator is simply an instrument showing by graphic 
diagrams the variations of the pressure in the engine cylinder of steam, 
gas, air, or whatever the working substance may be. Before James Watt 
invented the engine indicator (about 1814) he had already used a steam 





Fig. 97. — Watt's Original Steam Engine Indicator 
(Type of 1814). 



Fig. 98. — Section of 
Watt's Indicator. 



pressure gage on the cylinder of his engine, and since the movement of 
the piston in the early steam engines was very slow, he was able to 
observe with his eyes how the pressure varied during a stroke of the 
piston. In modern engines the movement of the piston is so rapid, how- 
ever, that a recording instrument is absolutely necessary. 

92 



ENGINE INDICATORS AND REDUCING MOTIONS 93 

Watt's indicator is illustrated in Figs. 97 and 98. It consists of a 
cylinder CC (Fig. 98) in which the piston P is moved against the resistance 
of the spring S by steam pressure from the engine cylinder, this pressure 
being exerted, of course, -on the lower side of the piston. A pencil at- 
tached to the upper end of the piston rod traces on a sheet of paper a 
diagram DD, of which the height on any ordinate is proportional to the 
pressure. The paper is moved back and forth on a slide by a string E 
moved in conformity with the piston. The instrument was of great 
service to Watt in perfecting his steam engines. In the modern indi- 
cators, of which a few of the best known makes are to be described, there 
are many improvements over the instrument used by Watt. 

Thompson Indicator. Of the engine indicators now in general use the 
Thompson is the oldest and best known. Fig. 99 shows one view of this 
instrument and Fig. 100 shows the corresponding sectional drawing. 




Thompson Indicator. 



It consists in essential parts of a piston 8 (Fig. 100) moving in a cylin- 
der 4. This piston is rigidly connected to the rod 12, which passes up 
through the cap 2. The motion of the piston rod 12 is transferred to the 
pencil 23 by means of suitable links designed to make the pencil move 
parallel to but usually four times as far as the piston 8. The maximum 
pressure of the pencil on the paper used for the diagram is adjusted by 
the thread and set-screw on the handle attached to the bracket X. 



94 



POWER PLANT TESTING 



The method of changing the springs in the various common forms of 
engine indicators should be well understood by everyone likely to be 
called on to " indicate " engines. When the work of changing springs 
is done clumsily or carelessly, a great deal of time is often wasted by the 

whole party engaged in the 
test. The method to be fol- 
lowed in changing springs of a 
Thompson indicator may be 
stated briefly as follows: The 
milled-edged cap 2 should first 
be unscrewed from the top 
of the cylinder containing the 
spring and piston. This cap, 
together with the sleeve and 
bracket X carrying the pencil 
lever and linkages, the piston 
rod, and the piston, can then 
be lifted from the main body 
of the indicator. By unscrew- 
ing the small milled-headecl 
screw 19 connecting the piston 
rod with the pencil arm the 
spring can then be unscrewed, 
first from the cap 2 and finally 
from the piston 8. By exactly 
reversing the operation another 
spring can be put in the place of the one removed. Changing springs 
in this instrument is a simple operation. No wrenches or other tools 
are required. Care should be taken, of course, to screw up the spring 
firmly against both the cap and the piston. Probably one-half the 
troubles with indicators in operation arise from loose springs, although 
not so often, probably, with Thompson indicators as with some other 
types. The height of the pencil can be adjusted by turning the screw- 
head 19 up or down on the piston rod. 

As a general rule, the spring selected for an indicator should be of such 
a scale that the largest diagram to be taken will not be more than 
If inches high; that is, if the maximum pressure will be about 140 
pounds, a spring with a scale of 80 pounds per square inch should be 
selected. Instruction books going with indicators have usually tables 
showing the spring recommended for a given maximum pressure. Gener- 
ally a higher card is permissible for light springs and slow engine speeds 
than for stiff springs and high speeds. The tension of the spring 31 in- 
side the drum carrying the paper for the diagram is varied by loosening 




Fig. 100. — Section of Thompson Indicator. 



ENGINE INDICATORS AND REDUCING MOTIONS 95 

the thumb nut and turning the large milled cap until the proper adjust- 
ment is secured. 1 

Crosby Indicators. For high-speed engines and for accurate results 
the Crosby indicator has long been a favorite with engineers. This in- 
dicator is illustrated in Figs. 101 and 102. It consists of a piston 8 
moving in the cylinder 4, and is connected by means of the piston rod 
10 and the link 14 to the pencil lever 16. All of the pencil mechanism 
(arranged to move the pencil point 23 in a straight line parallel to the 




Fig. 101. — Typical Crosby Indicator. 

motion of the piston 8) is supported by the links 13 and 15 on the sleeve 
3. The indicator spring is fastened at its lower end to the piston by a 
ball-joint and at its upper end it is screwed into the cap 2. The method 
of attachment of the springs to the piston by means of the ball-joint is 
shown more in detail in Fig. 103. 

In this indicator the spring is changed by first unscrewing the milled 

1 Unless there is a very good reason for a change in the tension of the spring in the 
drum it should not be altered. Particularly in indicators which have been used a long 
time the pin holding the spring in place is likely to be much worn, so that if adjusted 
often the spring may get loose, and then there is usually considerable difficulty in get- 
ting it again into its proper position. 



96 POWER PLANT TESTING 

cap 2, then this cap, the sleeve 3, the piston rod 10, and the connected 
parts can be removed from the cylinder 4. By unscrewing the spring 
by hand from the cap, which, of course, must be prevented from turn- 
ing, and also from the screw on the swivel head 12, the piston, the spring 
and the hollow piston rod 10 are detached from the other parts. A 
socket-wrench of the special form provided in every indicator box of 
this make is to be slipped over the piston rod to engage with the small 
nut shown (at 10) in Fig. 102 at the lower end of the piston rod. Then the 




Fig. 102. — Section of Crosby Indicator. 

piston rod is readily unscrewed from the piston and at the same time the 
spring is released from its attachment to the piston. Now with the pis- 
ton rod still in the socket of the wrench, slip the spring to be used over 
the piston rod until the head of the spring rests in the concave end of 
the rod. To do this, the wrench must be held upright, and then if the 
piston is inverted, or, in other words, if it is held so that the end screw- 
ing into the piston rod points downward, the piston rod is ready to be 
screwed into the piston, so that the transverse wire of the spring pass- 
ing through the bead will be held firmly in the slotted portion of the 



ENGINE INDICATORS AND REDUCING MOTIONS 99 

changed when the thumbscrew at the top of the central spindle has 
been unscrewed. 

In Fig. 105 a slightly different outside-spring arrangement is shown. 
It is distinguished particularly from Fig. 104 in having the indicator 
spring in compression instead of being 
in tension as in most other outside- 
spring types. The obvious advantages 
of the designs having the springs in 
tension are that springs can be changed 
much more readily than in other types; 
and that it is practically impossible if 
the springs and piston are well made 
for the spring to buckle over and bind 
the piston as happens frequently in all 
types having the spring in compression. 

The weakness of the designs having 
the spring in tension is in requiring a 
very long and slender piston rod which, 
being in compression, may have a ten- 
dency to buckle over and produce vari- 
able errors. As regards temperature 
effects, one arrangement is about as 
good as the other. 

Star Brass Indicator — Navy Pattern. The indicator called the 
" Navy Pattern," manufactured by the Star Brass Co., is shown in 
Fig. 106. In general principles of construction it is like the Crosby in- 
dicator illustrated in Fig. 104. The most essential difference is in the 
type of straight-line parallel motion for the pencil lever. It will be 
observed that this is practically the same as that used in the Thompson 
indicator (Fig. 99). 

Tabor Indicator. 1 In the form in which it is now manufactured the 
Tabor indicator, Fig. 107, differs from indicators like the Crosby par- 
ticularly in the means employed for producing a straight-line parallel 
motion for the pencil. In this device a roller is attached to the pencil 
lever and is arranged to move in curved slots on the inside of the rectan- 
gular box-shaped part shown in the figure. 

As regards the point of flexibility in the mechanism, this is not be- 
tween the spring and the piston, but, more like the Thompson, is in 
the ball and socket joint between the piston and the piston rod. Details 
of this construction are shown in Fig. 108. 

The principal precaution to observe in the use of this indicator is to 




Fig. 



105. — " Compression " Type of 
Outside Spring Indicator. 



Ashcroft Mfg. Co., Liberty Street, N. Y. 



100 



POWER PLANT TESTING 




Fig. 106. — Star Brass Indicator — Navy Pattern. 




Fig. 107. — Tabor Indicator. 



ENGINE INDICATORS AND REDUCING MOTIONS 101 

be certain at all times that the roller on the pencil lever moves freely in 
the curved slots. 

Outside spring types of this indicator are also made. 

To Change the Spring. The cylinder cap must be first unscrewed, 
and then this cap, together with the piston, spring, and connected parts 
can be lifted from the cylinder of the indicator. By removing the small 
screw under the piston the latter can be unscrewed from the lower end of 




Fig. 108. — Section of a Tabor Indicator. 



the spring. The other end of the spring can then be unscrewed from the 
cylinder cap. Another spring is put. into the indicator by slipping it 
over the piston rod with the end stamped T uppermost, screwing this 
end into the cylinder cap and screwing the piston to the lower end. The 
pencil mechanism must be moved downward until the piston rod enters 
the piston and the square shoulder enters the corresponding square 
socket in the piston. In this last operation care must be taken that 
the rod is firmly and accurately in the hole, and then the screw at the 
bottom of the piston should be firmly applied. 



102 



POWER PLANT TESTING 



3RL 




Section of Trill Indicator. 



To Change the Tension of the Spring in the Drum. The drum itself 
is first removed. Then after loosening the knurled nut on the central 

shaft and after the drum carriage 
has been lifted clear of the stops, 
the carriage can be turned in the 
required direction to secure the 
necessary tension and it can then 
be replaced by lowering into the 
stops. Care must be taken also 
that a firm grasp on the drum 
carriage is not lost, otherwise the 
spring will become uncoiled and 
probably also detached. 

Fig. 109 shows a section of a 
Trill outside-spring indicator. 1 In 
principle it is very much the same 
as the one shown in Fig. 105. Im- 
portant parts are labeled with their 
proper names, which should be 
studied. 
Bachelder Indicator. 2 Fig. no illustrates an engine indicator which 
is in many essential parts entirely different from all the types already 
described. It is so simple in construction that scarcely any description 
is necessary. The most radical difference is, however, in the form of 
spring used. This is a flat bar and is arranged with a movable fulcrum 
which can be adjusted to change the scale of the spring. Although a 
wide range is obtainable in this way, it has been found unsatisfactory to 
attempt to use a single spring for all the ranges from the highest pres- 
sures to low vacuums. On this account at least two springs, one for 
high and the other for low pressures, are usually supplied. On account 
of its heavy parts it is not suitable for high speeds. 

Springs are changed by first removing the taper screw shown at the 
extreme right-hand side in the figure, and then after unscrewing a cir- 
cular cap on the side of the cylinder the pin connecting the spring to 
the piston rod can be withdrawn with a small pliers or similar instru- 
ment. Usually before the spring can be withdrawn the thumbscrew 
attached to the movable fulcrum must be loosened. In the ordinary 
operation of the instrument the piston is not removed. 3 

1 Trill Indicator Co., Corry, Pa. 

2 Richard Thompson & Co., 126 Liberty Street, New York. 

3 When the spring is calibrated, the piston should be taken out so that a little 
cylinder oil can be put on it. It is not so necessary for this type when in use on a 
steam engine, as the oil in the steam will usually provide sufficient lubrication ex- 
cept when the steam is superheated. 



ENGINE INDICATORS AND REDUCING MOTIONS 103 

The principal difficulty with indicators of this type is that, there is 
always some uncertainty about getting the fulcrum set at exactly the 
right point. Also if the fulcrum slides easily it may shift during a test. 
The only safe way is to examine the setting of the fulcrum frequently 
throughout all tests. 

The spring on the drum is conical in form and is adjusted in practi- 
cally the same way as in the Crosby indicator. 




Fig. 110. — Bachelder Indicator. 



Precautions for Care of an Indicator. Unless an engine indicator is 
well taken care of, very soon it will be in a condition in which no 
reliance can be placed on results obtained with it. That the necessary 
precautions should be taken is all the more important, because it is one 
of the most expensive as well as the most delicate instruments used 
by an engineer in his ordinary practice. The following precautions are 
particularly important: 

1. Before an indicator is used all the working parts, especially the 
piston, should be carefully cleaned. Then after a spring suitable for 
the pressure has been attached in its proper position and a little cylinder 
oil has been smeared in a thin coat on the working surface of the piston, 
the parts should be replaced. Moving parts of the pencil mechanism 
should be oiled occasionally with watchmaker's or porpoise oil. It is a 
very good practice, especially when comparatively new indicators are 
being used on long tests, to take out the piston of the indicator fre- 



104 POWER PLANT TESTING 

quently and smear it with cylinder oil. For lubricating this piston it is 
a little better to use a comparatively thin cylinder oil of high flash test 
(like gas-engine oil) than one that is very viscous. 

2. Adjust the screw on the handle provided for moving the pencil so 
that when the pencil is sharp the application of the usual pressure on the 
handle will give a very fine line. 

3. Adjust the length of the indicator cord so that the drum will be 
neither too loose nor too tight; or in other words, so that the drum will 
not strike either of the stops when the engine is operating. On a small 
engine this is most easily tested by observing the diagram when the 
engine is on each of the dead-centers. If the diagram is either too long 
or too short the drum will not be moved the required distance, and the 
indicator diagram will be correspondingly too short and therefore inac- 
curate. The cord used should be selected with care. It must be of 
such a quality as not to be stretched appreciably by the forces to which 
it is subjected. For accurate work and on long-stroke engines fine an- 
nealed steel or phosphor-bronze wire, or indicator cord wit'h a wire core, 1 
should be used. The length of the cord should be adjusted very care- 
fully and fastened securely so that it will not slip or stretch so as to bring 
the drum up against one of the stops, making the diagrams too short. 
This effect can^usually be detected by the clicking sound of the drum 
striking the stop, if there is not too much noise in the room. The experi- 
enced engineer, however, will by force of habit invariably put his finger 
now and then during a test on the top of the drum or on the side of 
the bracket supporting it to determine whether its operation is satis- 
factory. Another way to determine a faulty adjustment on the usual 
crank-shaft type of engine 2 is to measure the lengths of the indicator 
diagrams. If the cord stretches the diagrams will be variable in length. 

4. The atmospheric line should always be taken preferably after the 
diagram has been made. It is drawn, of course, when the indicator cock 
is closed. By this order of procedure in tests, the diagram can be 
more easily taken exactly " on the signal." The length of the diagram 
must alvays be measured on the atmospheric line or on a line parallel 
to it. The indicator cock should be kept closed and the cord to the 
reducing motion should be unhooked except when a diagram is to be 
taken. When the cord is unhooked the drum should not be permitted 
to snap back against the stop. By observing these precautions the useful 
life of an indicator can be much prolonged. 

1 This indicator cord with a wire core which is guaranteed not to stretch in ordinary 
use can be obtained from the Athletic Store, State College, Pa. It is the most satis- 
factory indicator cord obtainable. 

2 In an engine without a crank-shaft like a direct-acting steam pump the length of 
the stroke and consequently of the indicator diagram is likely to be quite variable. 



ENGINE INDICATORS AND REDUCING MOTIONS 105 

5. Immediately after a diagram has been taken it should be removed 
from the drum and examined. If there are unusual irregularities in 
the lines, unaccountable differences in the areas or in the lengths of 
different cards, the facts should be noted and the best efforts should be 
made to remedy the faults. Irregularities are usually due to stretch- 
ing of the indicator cord, grit on the piston, lost motion in the working 
parts (usually inside the indicator cylinder) or excessive friction caused 
by overheating of the piston, particularly when used on gas engines. 

To correct these faults concerning the piston it must be removed from 
the cylinder and should then be carefully cleaned and again lubricated 
with cylinder oil. Before putting the piston and connected parts back 
into the indicator cylinder it' should be observed whether or not all the 
parts are connected firmly and without lost motion. 1 

6. After a test, the indicator should be removed immediately from 
the engine, protecting the hands with waste or thick gloves to prevent 
burns. All the parts, especially those in the cylinder, should be thor- 
oughly cleaned and then put together again without the spring, which 
should be put away with the other springs in a box provided for the indi- 
cator. An indicator should never be handled by taking hold of the drum, 
as usually it is fastened to the indicator by only a loose slip joint, and this 
comes off easily. 

7. Before opening the indicator cock to take the first diagram in a 
test, examine the indicator carefully to see that piston, spring and pencil 
mechanism are attached securely. A good method is to take hold of the 
end of the pencil lever near the pencil-point and try to move it up and 
down. If there is no lost motion observable and the pencil-point seems 
to be at about the right height for drawing the atmospheric line, it may 
be assumed that the indicator has been assembled properly. Otherwise 
it will be observed immediately by this test if the indicator has been put 
on the engine without inserting a spring, or if the milled nut at the top 
of the indicator cylinder has not been firmly screwed down. Observe 
also whether the " union " nut attaching the indicator to the cock is 
held by at least three or four good threads. Otherwise if this nut slacks 

1 One of the causes of errors in results obtained with indicators not so readily de- 
tected is due to the pencil motion not being parallel to that of the piston in the indica- 
tor. A simple test for this 'is to draw an atmospheric line on a card placed on the 
drum. The card should be at least as wide as the height of the drum. Then after 
taking out the spring raise the pencil to the full height of the card by pressing lightly 
on the piston. This operation should be repeated several times at several points along 
the length of the card. To secure the best accuracy it is desirable to "block" the 
drum in each position. If the lines drawn are exactly perpendicular to the atmos- 
pheric lines there is no error in the pencil mechanism. If the test for perpendicularity 
is made by a triangle and straight edge, it should be done with the triangle first lying 
on one side and then on the other, to eliminate any inaccuracy in it. Often the triangles 
used by engineers are very inaccurate. 



106 POWER PLANT TESTING 

back a little the whole indicator may be thrown by the f orce 1 of the steam 
pressure against the ceiling of the room. More indicators are worn 
out and broken by careless assembling than in any other way. 

8. One of the best ways to put an indicator card on the drum is to 
first bend over one of the short edges of the card on a line about a quarter 
inch from the end and place this end with the line of bending snugly 
against the top of the longer clip on the drum. Then lap the card around 
the drum and insert the other end of the card into the upper end of the 
shorter clip. The card should then be pushed down to the stops in the 
clips, being careful however to keep it tight and straight, so that there 
will be no wrinkles. Finally to prevent the card from shifting on the 
drum, the end of the card under the shorter clip should be bent over 
carefully and firmly. 

SPECIAL TYPES OF ENGINE INDICATORS 

Cooley-Hill Continuous Indicator. For many purposes of investiga- 
tion it is very important to have continuous records showing the varia- 
tions of the cycles in the operation of an engine. Many devices have 
been used for this purpose, but as the motion was taken from the crank 
shaft there was no simple relation between points on these diagrams and 
the corresponding points in the stroke of the engine. Furthermore, 
because of the difficult relation, such cards could not be measured with 
a planimeter. Similar apparatus for the same purpose operated by an 
electric motor were open to the same objection. To overcome these 
difficulties a continuous indicator was developed in which the motion 
was proportional at every instant to the movement of the piston. With 
a diagram obtained with this instrument it is not difficult to determine 
the dead-center following release, and the conventional indicator card 
for an engine is then readily obtained by turning the diagram for the 
complete cycle back on itself by folding the card or ribbon at this dead- 
center. If transparent paper is used, the complete diagram can be seen 
with all the points in their true relative positions as regards the move- 
ment of the piston. The indicated horse power can then be readily cal- 
culated with the aid of a planimeter. This continuous indicator is 
illustrated in Fig. in. The indicator cylinder C, the piston, and the 
pencil motion may be of any standard make, as the collar M, for attach- 
ing the drum mechanism, is adjustable in size so that it can be fitted 
to indicator cylinders of different diameters. By this arrangement only 
one drum motion need be provided for using this indicator motion on a 
number of types of indicators such as would be required for use with 
steam engines, gas engines, high-pressure air compressors, ammonia 
compressors, etc. In this apparatus the drum D moves forward a given 
amount with every stroke of the engine. The indicator cord S is con- 



ENGINE INDICATORS AND REDUCING MOTIONS 107 

nected to the indicator reducing motion and is driven by being connected 
in the usual way to the cross-head of the engine. 

The mechanism operating the drum motion is illustrated in Fig. ma. 
It consists essentially of two miter wheels B and C, meshing with a similar 
wheel E, to which the pulley W, carrying the indicator cord, is attached. 
At the top of the wheel B and at the bottom of C are so-called silent 




Fig. 111. — Coolev-Hill Continuous Indicator. 



ratchet clutches a, a, each of which operates in only one direction to grip 
the collars concentric with the wheels B and C. Only one of these collars 
is shown in the figure. Both are rigidly attached to the central spindle 
J, carrying the indicator drum D (Fig. in). For example: This central 
spindle is gripped by the ratchets a, a in the wheel B, during the " for- 
ward" stroke of the engine, and is released during the " backward" stroke. 
The ratchet in the wheel C, on the other hand, grips this same spindle 
during the "backward" stroke and releases on the "forward" stroke. 



108 



POWER PLANT TESTING 



In this way the drum D is constantly moved on the spindle J in the same 
direction. Neither of the wheels B nor C is directly attached to the cen- 
tral spindle, and they can move it only when they move in the direction 
in which they grip their ratchets a, a, engaging in the grooves g, g. 

The miter wheels B and C are con- 
nected to each other by means of a 
spiral spring enclosed in the casing D. 
This serves the function of the ordi- 
nary drum spring in the usual type of 
indicator for bringing the drum and 
cord back when the cross-head moves 
toward the indicator. 

Optical Indicators. The usual types 
of indicators operating with a piston 
are not suitable for engines running at 
much over 400 revolutions per minute. 
For higher speeds optical indicators are 
used. These operate by the deflection 
of a beam of light from a mirror, the 
deflection being proportional at any in- 
stant to the pressure. When such a 
device is used on an engine successive 
indicator diagrams can be readily ob- 
served and compared by marking with 
a pencil the reflection upon a ground- 
glass plate, and if a photographic sensi- 
tive plate is exposed to the beam of 
light in the place of the ground glass, 
a permanent impression can be taken, 
showing at any instant the operation of 
the engine. Optical indicators are prac- 
tically the only kind that can be used successfully for indicating the 
action of modern high-speed automobile engines. Every well-equipped 
automobile testing plant should be provided with one of these instru- 
ments. One of the simplest and best apparatus of this kind is illus- 
trated in Fig. 112. The indicator is shown in the picture vertically above 
and connected to the head of the engine. Steam pressure is communi- 
cated to the instrument through the usual type of indicator cock sup- 
porting it. A system of levers shown (a simple reducing motion) serves 
for reducing the length of the stroke of the engine to a suitable size for 
such a small instrument. A glass mirror moved about a vertical axis by 
the motion transmitted from the cross-head and about a horizontal axis 
by the pressure in the engine cylinder reflects a beam of light from 




Fig. Ilia. — Details of Cooley-Hill 
Indicator. 



ENGINE INDICATORS AND REDUCING MOTIONS 109 

a lamp upon a sheet of paper so that the indicator diagram can be traced. 

Details of the essential parts of this instrument are shown in Fig. 112a. 

Through the indicator cock the pressure in the engine cylinder is com- 




Fig. 112. — Perry's Optical Indicator. 



This pressure tilts the mir- 




municated to the cored passages marked A, A. 
ror B, attached to the thin steel 
diaphragm D. When, there- 
fore, the mirror is still, a ray of 
reflected light will be seen as a 
bright spot on the screen; but 
when moved both by the pres- 
sure and the motion of the 
cross-head the conventional in- 
dicator diagram is traced. It 
is very interesting to watch 
the rapid change of shape of 
such diagrams as load, speed, 
pressure, cut-off, etc., are 
changed. With such an instru- 
ment these interesting phenom- 
ena in engine operation can be illustrated on a ceiling to a large class of 
students. 




Fig. 



112a. — Essential Parts of Perry's Optical 
Indicator. 



110 



POWER PLANT TESTING 



Another type of optical indicator intended particularly for high-speed 
automobile engines is shown in Fig. 113. In this instrument the move- 
ment of the beam of light is produced by reflection from a small mirror M 
arranged to move in two distinct planes at right angles to each other. 
In one plane the movement of the piston is accurately reproduced, and in 
the other plane the movement is proportional to the pressure. Either of 
these movements or deflections of the mirror, taken alone, would cause 
the reflected beam of light to trace on the ground-glass plate a straight 
line; that due to the pressure being arranged to produce a straight verti- 
cal line and that due to the motion of the piston a straight horizontal 
line. But obviously the two movements taken together trace a diagram 



Ground Glass Plate 




Fig. 113. — Section of a "Manograph" Optical Indicator. 



indicating at any instant the pressure in the engine cylinder for the cor- 
responding position of the piston. A flexible shaft, attached at one end 
to the crank shaft of the engine, moves the disk A and with it the crank 
C, as well as the small lever L attached to it. The free end of this lever 
is arranged to turn the mirror M about a vertical axis by means of the 
small strut a, while the pressure exerted on the diaphragm D, as trans- 
mitted from the engine cylinder by the pipe P, moves the mirror about 
a horizontal axis by means of the strut b. In this apparatus the dia- 
phragm takes the place of the piston and spring in the ordinary type of 
indicator. These diaphragms, like those used in pressure gages (see page 
11), can be made of such thickness that a diagram of satisfactory size can 
be obtained for high or low pressures. When the diaphragms are care- 
fully calibrated, a reasonable degree of accuracy can be expected. The 



ENGINE INDICATORS AND REDUCING MOTIONS 111 



l^J 



relative motions of the mirror in the two planes are set in phase by ad- 
justing the milled screw S, operating a small worm wheel serving for 
changing the angular position of the crank disk A, to make the move- 
ment of the mirror about the vertical axis correspond with that due to 
the pressure. There are various methods for determining the proper 
adjustment for correct " phase rela- 
tion," but the simplest is to break the 
ignition circuit on the cylinder to be 
indicated when the engine is operating. 
The compression curve will then prac- 
tically coincide with the expansion line 
when the adjustment is correct. The 
principle of operation is shown more 
clearly in the diagrammatic sketch of 
Fig. 114. Parts are indicated by the 
same letters as for Fig. 113. Fig. 115 
shows the apparatus as it would be set 
up for indicating an engine. A dia- 
gram taken from a gasoline automobile engine is shown in Fig. 116. 

The Hopkinson optical indicator is shown very clearly in Fig. 117. 
It is essentially similar to the manograph, except that it has a piston F 
instead of a diaphragm and a direct type of reducing motion is used as 
shown in Fig. 117a. 

The long tubes connecting the " manograph " type with the engine 
cylinder are very likely to introduce considerable errors. The time lag 
between the pressure in the cylinder and that at the diaphragm is very 




Line Diagram of "Mano- 
graph." 



Acetylene 




Ground 



-Top of Tripod Stand 



Fig. 115. — "Manograph" Ready for Attachment to Engine. 



appreciable at high speed. This error is largely eliminated by adjusting 
the cyclic relations so that the compression curve observed when the 
spark is cut off is in phase with the expansion line. But the long 
tube also throttles very considerably the pressures of the gases and in- 
creases the effective clearance of the cylinder. To eliminate these diffi- 
culties an ingenious gear device is inserted between the engine shaft 



112 



POWER PLANT TESTING 



and the small crank R. By this means the crank R can be retarded behind 
the engine crank by any phase difference that is necessary. This retard- 
ation varies, however, with the speed of the engine and the adjustment 




Fig. 116. — Indicator Card taken from a High-speed Automobile Engine with an 
Optical Indicator. 




Fig. 117. — Hopkinson's Optical Indicator. 

must be made every time the speed is changed in order to get accurate 
diagrams. 

Calibration of Indicator Springs. The pistons of engine indicators 
are invariably made of a very definite area, usually one-half square inch ; 
and it is possible to calibrate the deflection of the springs with respect 



ENGINE INDICATORS AND REDUCING MOTIONS 113 

to this area, so that a certain definite pressure per square inch 1 in the 
cylinder will correspond to a definite deformation of the springs. In 
English units the pressure on the piston in pounds per square inch cor- 
responding to a movement of the indicator pencil on the diagram of one 
inch is called the scale 2 of the spring. Indicator springs should always 
be calibrated by the makers. The calibration should be made when 
they are in the indicator in which they are to be used. 

Short Brass Slecvo Soldered to WIro 
1 Screwed wilh 2 Clamping Nuts 




String to Crosahcad or Pump Rod 
Le?er Pkotled ~" " 



Fig. 117a. — Reducing Motion for Hopkinson's Indicator. 

Cooley Apparatus for the Calibration of Indicator Springs. An ap- 
paratus similar to the one designed by Professor M. E. Cooley is very 
generally used for the calibration of indicator springs. One of the latest 
and more elaborate forms of this instrument is shown in Fig. 118. In 
its essential parts this apparatus consists of a small cylinder C, sup- 
ported on a bracket B, a connection I at the top of this cylinder for the 
attachment of the indicator to be tested, and a stuffing-box or gland at 
the bottom of the cylinder into which a plunger-piston P is fitted. The 
lower end of this plunger rests on a sensitive platform scales. Any 
pressure in the cylinder C can therefore be weighed. Steam may be 
admitted to the cylinder through a pipe E, and is exhausted through the 
pipe A. By adjusting the globe valves on the pipes A and E any pressure 
desired can be secured in the cylinder C, and this same pressure is, of 
course, exerted both on the piston of the indicator above and on the 
plunger P below. This plunger is usually made with an area of one-half 
square inch. For a plunger of this area, then, if for a given pressure the 
scales balance at 10 pounds, the pressure in the cylinder C, and on the 
piston of the indicator, is 20 pounds per square inch. To eliminate friction 3 

1 Indicators are always designed to relieve the pressure above the piston due to 
leakage around it, so that on this side there is always atmospheric pressure. 

2 Instead of "scale" the word "number" is often used. That is, a spring of which 
the scale is 40 pounds would be called "No. 40." 

3 The operation of the apparatus is usually much improved by pouring, just before 
the steam valves are opened, a few drops of cylinder oil into the cylinder C through I 
to lubricate the plunger. 



114 



POWER PLANT TESTING 



as much as possible, the plunger P should be kept spinning when obser- 
vations are being taken. For this purpose a hand wheel K with con- 
siderable mass, for its " fly-wheel " effect, is provided on the shaft of the 
plunger. A more uniform motion of the plunger is obtained, however, 
by having the hand wheel grooved to take a small belt to be driven by 
an electric motor M. The plunger is supported usually on a ball-bearing 
joint set in a low pedestal L. 

By connecting a pipe E to a suitable manifold or similar fitting, to 
which are attached three separate pipes supplying respectively steam, 
air, and water under pressure, an indicator can be tested with varying 




Fig. 118. — Apparatus for Calibrating Indicator Springs. 



pressures under the actual conditions in service; that is, when used for 
steam, air or water. American engineers always prefer making calibra- 
tions of indicators under conditions as nearly as possible those pertain- 
ing to their ordinary use. The Power Test Committee of the A.S.M.E. 
recommends also the following procedure: 

To bring the conditions approximately at least to those of the working indicator, the 
steam should be admitted to the indicator in as short a time as practicable for each of 
the pressures tried, and then the indicator cock should be closed and the steam ex- 
hausted before another pressure is tried. By this means the parts are heated and 
cooled as under working conditions. For each required pressure open and close the in- 
dicator cock a number of times in quick succession, then quickly draw the line for the 




ENGINE INDICATORS AND REDUCING MOTIONS 115 

desired record, observing at the same instant the "reading" of the standard used for 
comparison. A corresponding atmospheric line is to be taken immediately after each 
pressure line. 

Indicator springs for gas and oil engines should also be calibrated with the indica- 
tor in as nearly the same condition as to temperature as exists when it is in use. A 
simple way of heating recommended is to subject it to steam pressure just before cali- 
bration. Compressed air is a suitable fluid for the actual calibration, being preferred 
to steam as it brings the conditions as nearly as possible to those of practice when the 
indicator is in actual use in gas or oil engines. 

In Europe an apparatus like Fig. 119 is used a great deal. It is essen- 
tially the same as the dead-weight gage testers described on page 17, 
except that there is a connection for an indi- 
cator. Pressure is applied by loading weights 
on the platform P resting on the plunger. In 
this apparatus the gage G serves merely as 
a means of checking and avoiding mistakes. 
American engineers object to this method be- 
cause the calibration is made when the indi- 
cator is under nothing like the conditions of 
service, at least as regards temperature. Many 
engineers calibrate their indicators by compar- Fig. 119. — Dead-weight 
ing them with a good test-gage which has been Tester for Indicator Springs, 
carefully calibrated with a dead-weight tester. 

The gage and indicator are put on the same pipe carrying high-pressure 
steam. The movement of the pencil of the indicator is carefully ob- 
served, and compared with the reading of the gage. This latter is the 
method suggested by the Power Test Committee of the A.S.M.E. in 
their report in Nov., 1912. 

A simpler form of the Cooley apparatus intended for the so-called 
" dry method " of testing is shown in Fig. 120. A suitable fitting for 
receiving the indicator I is supported on the bracket B. The legs of 
this bracket span over a sensitive platform scales S. A small rod R 
rests at its lower end on a small pedestal standing on the platform of 
the scales S. On the top of this rod there is a cap supported on a small 
conical bearing to give some flexibility. This cap is made to fit easily 
into the lower side of the piston in the indicator. The indicator itself is 
attached to the top of the hand wheel W. Then when the hand wheel 
is screwed downward the indicator comes down with it and compresses 
the indicator spring. At the same time a pressure is exerted on the 
rod R which can be balanced on the scale beam. When a force is ap- 
plied to compress the spring in the indicator, the magnitude of the 
force can be determined by weighing the pressure on the scales. If the 
area of the piston in the indicator is one-half square inch, then twice 
the weight on the scales is the pressure exerted in pounds per square 



116 



POWER PLANT TESTING 



inch. Heat can be applied to the indicator by passing steam through 
a rubber or flexible copper tube wrapped around the cylinder. 1 

Method for Calibration of Springs. After cleaning the internal parts 
of the indicator, inserting the spring to be calibrated, and oiling the 
piston with cylinder oil, the indicator is to be attached to the indicator 
cock on the calibrating apparatus. Before putting the card on the in- 




Fig. 120. — Apparatus for "Dry" Method of Indicator Testing. 



1 Some engineers, particularly in Germany, advocate that an indicator should be 
slightly jarred just before each calibration line is drawn, intending that this jarring is 
equivalent to the vibrations which an indicator receives when in service on an engine. 
Since, however, readings are taken with both increasing and decreasing pressures it is 
doubtful whether this additional work is necessary on an apparatus like Fig. 118. If 
on the other hand a dead-weight tester like Fig. 119 or the method of comparison with 
a test gage (page 115) is used, tapping both the indicator and the gage is probably 
very advisable. 



ENGINE INDICATORS AND REDUCING MOTIONS 117 

dicator drum on which the record is to be made, two approximately 
parallel and vertical lines should be drawn on it about one-half inch 
apart, similar to the lines AB and CD in Fig. 121. Meanwhile the indi- 
cator should be thoroughly warmed if a calibration with steam pressure 
is to be made. Then with the indicator cock and the valve on the 
steam pipe E (Fig. 118) closed and the exhaust pipe A open, draw the 
first calibration line on the card. This should be made by setting 
the pencil point at D, and then by pulling the cord attached to the drum 
draw a line crossing the vertical line AB. With springs of which the 
scale is 40 pounds or less, a similar record should be made for incre- 
ments of every 5 pounds per square inch change in pressure, while for 
higher scales the increments may be made 10 pounds. If with in- 



Na^j?__ Hnur /. '.T<?/? M. .. 




,. /•/sum© 




Which En 
B. Press _ 
Vac. gaug 

Kevs. 

Spring 


a 




A 




C 


Area 

M. Ord 

M.E.P.. 

l.H.P, 


e 




















































' 






















Up 




Down 






—-"Atmospheric" Lines 
D OBS 




INDICATG 


R NO. 
O 




B 




ERVER: ^^ 

Mfd. 



77 

Fig. 121. — Sample Card Illustrating a Test of an Indicator Spring. 



creasing pressures the lines are drawn toward the left, then with de- 
creasing pressures they should be drawn toward the right with equal 
increments, beginning at the opposite vertical line AB. By this method 
the corresponding lines for equal pressures will be immediately over 
each other between the two verticals. With an accurate scale, gradu- 
ated preferably to one one-hundredths inch, measure between AB and 
CD the distance from the atmospheric line first drawn to the various 
" pressure lines," and record the results. Care should be taken that 
with the increasing increments the pencil rises to the required pressure 
and that with decreasing increments it falls to these pressures. In 
other words, if when the lines for increasing pressures are being drawn, 
the pressure rises too rapidly to draw the line at the proper time when 
the scale beam is just balancing, then the pressure should be again re- 
duced below the value required, so that the pencil will be again ascend- 



118 



POWER PLANT TESTING 



ing when the line is drawn. Similarly for decreasing pressures, if the 
pressure gets too low, it must be increased and again brought down to 

the required value. 1 If the 
results obtained do not seem 
to be consistent, the diffi- 
culty is probably due to 
passing the required pres- 
sure so rapidly that the lines 
have not all been drawn at 
the proper time. 

The difference between 
the lines for increasing and 
decreasing pressures shows 
the amount of friction and 
lost motion in the indica- 
tor. 2 The error of the in- 
strument is obtained by 
comparing the mean or- 
dinates of the card thus 
obtained with the actual 
pressures as determined 
by weighing. From time 
to time the accuracy of the 
platform scales should be 
determined by testing with 
standard weights. For de- 
pendable results two calibrations, each " up and down," should be made 
for each spring and the results compared. 

When indicators are used for pressures which are never less than 
atmospheric, the springs are in compression and apparatus of the form 
described are satisfactory; but when indicators are used on the low- 
pressure cylinders of engines, the springs are usually in tension. For 
this service a slightly different device must be used for calibration. A 
suitable apparatus is shown in Fig. 122. 

The indicator I is supported on a bracket similar to the one used in 
the apparatus shown in Fig. 120. A short steel rod (about No. 18, 
B. & S. gage) is attached to the lower side of the piston in the indicator 
by screwing into a hole tapped centrally. Now if weights are suspended 

1 The same precaution must be observed in beginning the test. To be sure that 
the pencil and piston have not been falling instead of rising, the piston rod should be 
pushed down lightly before the atmospheric line is drawn. 

2 Half of this difference, to be more accurate, represents the friction and lost motion 
in any one position. 




Fig. 122. 



Apparatus for Testing Indicator 
Springs in Tension. 



ENGINE INDICATORS AND REDUCING MOTIONS 119 

from the end of this rod 1 the spring can be calibrated in tension by- 
drawing lines on a paper card placed on the drum in the same general 
way as when the spring was tested in compression. 

A suggested form for the arrangement of data for these calibrations 
is given below. 

Calibration of Indicator Spring (Compression) 

In Indicator No 

Rated scale of spring 

Diameter of piston of testing apparatus ins. 

Area of piston of testing apparatus sq. ins. 

Identification marks on spring 

Observers \ 



No. of 

Reading. 


Net Weight 

on Scales, 

Lbs. 


Actual 
Pressure on 

Piston, 
Ibs./sq. in. 


Ordinates or "Heights" 
Measured on Card, Inches. 


True Scale 
of Spring, 1 




Up. 


Down. 


Average. 


Remarks. 


1 


2 


3 


4 


5 


6 





















1 " The calibration of a spring should be made for at least five equidistant points. 
For ordinary work the arithmetical mean of the various results should be taken for the 
average scale." — Report of Power Test Committee of A.S.M.E. 

Curves. Results should be shown graphically for calibrations of in- 
dicator springs by plotting for abscissas the actual pressures in pounds 
per square inch and for ordinates the corresponding average height, 
inches, above the atmospheric line. Use very large scales as otherwise 
these curves are of little value. 

Calibration of Indicator Springs with the Mercury Column. The 
method to be followed in calibrating indicator springs with a mercury 
column is essentially the same as described on page 19 for the calibra- 
tion of pressure gages. After the indicator has been cleaned and oiled, 
it should be attached to the testing drum or cylinder by means of an 
indicator cock. Then while the indicator is being heated to the tem- 
perature of the fluid medium used (steam, air or water), the paper 

1 The weight of this rod and wires or strings supporting the weights must be added 
to them to get the correct tension. If, however, only the true scale of the spring is 
desired, as is usually the case, the weight of these parts need not be considered, pro- 
vided, of course, the atmospheric as well as the other lines are all drawn with these 
parts attached to the piston. 



120 



POWER PLANT TESTING 



card can be put on the drum after first drawing two vertical lines one- 
half inch apart, as explained when describing the apparatus shown in 
Fig. 118. Following these same instructions the atmospheric and other 
pressure lines are drawn first with increasing and then with decreasing 
increments. 

Testing the Drum Motion of Indicators. An apparatus for deter- 
mining the relative accuracy of the drum motion of indicators as regards 
uniform tension in the cord for a given speed is illustrated in Fig. 123. 




Fig. 123. — Brown's Apparatus for Testing Drum Motion. 

This device, known as Brown's, consists of a rod R, which is made to 
take the same movement as the end of the cord in a reducing motion by 
being attached through a connecting rod to a crank pin on a disk like 
the face plate of a lathe. At the other end this reciprocating rod is 
attached to a bell-crank lever F, of which the outer end P carries a 
pencil for making a diagram on a card attached to a vertical frame O. 




Fig. 124. — Diagrams taken from Apparatus for Testing Drum Motion. 

The short end A of the bell-crank is connected to a helical spring S 
and the other end of this spring is attached to an arm fitted on the rod 
R. To the end of the spring at A the indicator cord is attached, being 
of the same length as when in use on an engine. Now when the recip- 
rocating rod R is in motion and the tension in the spring S is uniform 
the pencil at P will describe a horizontal line. If, however, the tension 
in the indicator cord varies and consequently also the tension in the drum 
spring is not uniform, the pencil will describe a closed curve. Examples 
of such curves are shown in Fig. 124. Curve AB was obtained when the 



ENGINE INDICATORS AND REDUCING MOTIONS 121 

apparatus was moving very slowly, EF when operating at about 700 
revolutions per minute, and CD when the speed was about 250 revo- 
lutions per minute. The latter speed is obviously the one for which the 
stiffness of the spring in the indicator drum and the length and quality 
of the cord are most suitable. 

Brown's apparatus is useful merely in showing relative results and 
can be depended on scarcely at all for absolute or actual values. Pro- 
fessor Julian C. Smallwood has devised an apparatus shown in Fig. 125, 
from which actual values can be interpreted, as shown by the diagrams 
in Fig. 126. 1 When the drum and cross-head motions are exactly pro- 
portional the diagram traced is a straight inclined line, indicating no 
error in drum motion. Stretch of the cord and inertia of the drum 
and its spring cause a lack of proportionality. As a result when these 
phenomena exist a closed curve will be traced. The departure of any 
point on this curve from the straight line joining its uppermost and 
lowest points indicates the error of the drum motion. 

Reducing Motions or Driving Rigs for Indicators. In the case of 
most engines the length of the stroke is very much longer than the great- 
est possible movement of the drum of the indicator. It is therefore 
necessary to provide some means called a reducing motion, which pro- 
duces shorter movement, but which at every instant corresponds ex- 
actly with that of the cross-head. If this correspondence is not secured 
the length of the indicator diagram cannot be accurately reduced nor 
calculated, and the timing of the events or so-called " points in the 
stroke " will not be correctly represented. 

The most satisfactory reducing motion or driving rig for an indi- 
cator is some form of well-made pantograph (Fig. 127) with a driving 
cord of fine annealed wire or a linen cord with a stranded wire core. 
Although unstretchable cord is to be preferred, it is not always avail- 
able and ordinarily satisfactory results are obtainable with good hemp 
and linen cords if properly stretched in the process of manufacture. 

Reducing motion and the cord or wire connections to the indicator 
should be so perfect as to produce diagrams of equal length when 
the same indicator is attached to either end of the cylinder. Tests of 
the reducing motion should show also a proportionate reduction of the 
motion of the piston at every point of the stroke; that is, there should 
be a fixed ratio in every position between the actual proportion of the 
stroke passed through and the apparent proportion measured on the 
indicator diagram. 2 

1 For more complete description see Power, Aug. 20 and Sept. 24, 1912. 

2 To make this sort of test properly the diagram should be taken just before the 
engine is stopped at a point other than a dead-center, and this will serve as the basis 
of comparison with the measured length of stroke taken by the piston. The actual 



122 



POWER PLANT TESTING 




%mmm 



Elevation 
Fig. 125. — Smallwood's Drum Motion Tester. 



Overtravel of Drum 

at Crank End \^t 




Diagram from Smallwood's Drum Motion Tester. 



proportion of stroke moved through by the piston is measured by the distance the 
cross-head has moved compared with the full length of the stroke. Before making 
this measurement the slack should be taken up by putting enough steam into the 
cylinder to bring some pressure upon the piston, but not sufficient to start the fly- 
wheel. 



ENGINE INDICATORS AND REDUCING MOTIONS 123 

One of the commonest and most disastrous errors made in connect- 
ing up indicators is illustrated in Fig. 128, where an indicator cord is 
shown connected directly to the cross-head C. Obviously near the posi- 



*r"". 











Fig. 127. — Pantograph or Lazy-tongs Reducing Motion. 

tion C 2 the movement of the drum is much less for a given piston dis- 
placement than at Ci. The difficulty is remedied in Fig. 129 by using a 
pulley P to avoid unequal angularity of the part of the cord connected 



J 



l_ 


-""" ' 1 






0-" 




(o) r 


&' 










« 




^C. 






! 


1 





Fig. 128. — Incorrect Method of Con- 
necting Indicator Directly to Cross- 
head. 



3JT®r^l= 



Fig. 129. — Correct Method of Connect- 
ing Indicator to Cross-head. 



to the cross-head. Similarly unequal angularity in a marked degree of 
the part of the cord connected to the reducing motion must be avoided 
for the same reason. The cord must leave the reducing motion as 
nearly as possible in a line parallel to the axis of the cylinder. 



124 



POWER PLANT TESTING 



Pipes and cocks leading from the clearance space in the cylinder to 
the indicators should be as short and direct as possible. Except where 
no other device is practicable the use of a three-way cock and a single 
indicator for a double-acting engine (Fig. 161, page 139) is not consid- 
ered good practice. An indicator should be provided for each end for 
accurate work. The two indicators can be usually connected up to a 
single reducing motion in some such way as shown in Figs. 130 and 131. 




Fig. 130. — Simple Pantograph. 

Error produced by the use of three-way cocks is usually in increasing 
the area of the indicator diagram, due to the tardiness of the indicator 
in responding to the changes of pressure. 

One of the simplest forms of reducing motions is illustrated in Fig. 
132. This device is pivoted at one point A to a pedestal supported on 
the frame of the engine, and has a link BH connected to the cross-head. 
The indicator cord rides in a circular arc CD, proportioned to give the 




Fig. 131. — Approved Method of Connecting Two Indicators to One Reducing Motion. 

required movement to the drum of the indicator. Although this ar- 
rangement does not give an exact reproduction of the movement of the 
cross-head, yet if the pendulum AB and the cross-head are simulta- 
neously at the middle of their strokes and the position B is'as far below 
the horizontal drawn through H (Fig. 133) as the extreme positions F 
and F' are above it, the error is insignificant. An" improved type of 
this device is shown in Fig. 134, in which the cord rides in a groove on 



ENGINE INDICATORS AND REDUCING MOTIONS 125 



the circumference of a quadrant pulley. By attaching the pendulum to 
the quadrant pulley by means of a suitably designed " slip " joint or 
clutch, the pendulum can be disconnected from the quadrant so that 
the segment and the indicator cord will be moved only when the indi- 
cator diagrams are to be taken. 



c^ 



->C6rd to Indicator 



1 

i 




\ 








r® 


f— *\ ~™ 




y 








!=£ 


K 


<f 












I 




Fig. 132. — Simple Pendulum Reducing 
Motion. 



Fig. 133. — Approximately Accurate 
Pendulum Device. 



Brumbo's Pulley is also a form of reducing motion of the pendulum 
type. It is illustrated in Fig. 135. In this device a guide pulley is 
placed between the indicator and the quadrant pulley. A modified and 
simpler device of the same kind consists of an upper portion moving in 
a vertical direction in a swinging tube 
and a lower portion pivoted directly 
to the cross-head. In the arrange- 
ment shown in Fig. 135, the pin be- 
tween the segment and the indicator 
over which the cord passes is not ab- 
solutely essential in a temporary rig 
where no great accuracy is expected, 
as without it the change of angularity 
of the cord from one end of the stroke 
to the other is small. 

A very good and simple device is Fig. 134.— Maloney's Reducing Motion, 
shown in Fig. 136, consisting of two 

rods AB and BC, together with a pin D for the attachment of the indica- 
tor cord. If this is made so that AB = BC, then in any position of the 
arms the movement of the point D will be exactly proportional to that 
of the cross-head at C. The point A is fixed to the frame of the engine. 




126 



POWER PLANT TESTING 



The point B will always move half as far horizontally as C, because ABC 
is an isosceles triangle and the perpendicular drawn from B to the line 
AC bisects it. Then the horizontal movement of any point D in AB 



AD AD 

will be -r^r of that of B or — -r=r of the length of the stroke 
AB 2 AB 



Except for 
the very small change of the angularity of the cord as D goes from the 




Fig. 135. — Brumbo's Pulley. 

position i to 3, the motion of the indicator drum moved by this device 
will be perfect. 

Figs. 137, 138, 139, and 140 are illustrations of modified forms of 
pantographs, sometimes known as a " lazy-tongs." Because of the 
numerous parts of which they are composed, requiring a great number of 
joints, they are likely to be troublesome with high-speed engines. A plan 
view showing one of the methods of attachment of this device to a hori- 
zontal engine is given in Fig. 137. The obvious objections to the arrange- 



ENGINE INDICATORS AND REDUCING MOTIONS 127 



ment as shown are that there is more than the allowable angularity of 
the indicator cord between the pantograph and the pulley on the indi- 
cator, and that a single indicator is con- 
nected up by a three-way cock to both 
ends of a double-acting engine with a long 
stroke. 

The ones illustrated in Figs. 138, 139, 
and 140 are very commonly used. They 
are made usually of rods of iron or of steel 
nicely riveted together at the joints. The 
indicator cord is generally attached as at B 
(Fig. 138) and the ends A and C of the longer rods are fastened respectively 
to the cross-head and to the frame of the engine. It is a necessary 




Fig. 136. — Oscillating Arm Device. 




Fig. 137. — Plan View, Showing Attachment of Pantograph. 

requisite that in all these pantograph types the points corresponding' to 
A, B, and C shall lie in a straight line as shown, and DE must be equal 





Fig. 138. — Simple Par- 
allel Reducing Motion. 



Fig. 139. — Simple Parallel Reducing Motion 
as Attached to a Steam Engine. 



in length and parallel to FG. Then AF is in the same ratio to HF as the 
stroke of the piston is to the length of the indicator diagram. 



128 



POWER PLANT TESTING 



Fig. 141 illustrates another interesting parallel motion. It consists of 
a rod R, moving in a slide S, parallel to the piston rod. A link BD is 
attached to the slide R at B and to CE at D, while AE is fastened at one 
end to the cross-head. In this case again if A, B, and C are in the same 
straight line, then the following relation holds : AE : BD and CE : CD as 




Fig. 140. — Simple Pantograph Attached to an Air Compressor. 

the stroke of the piston is to the length of indicator diagram. The cord 
is hooked on a pin at H. It is sometimes desirable to have a separate 
pin for each indicator used. 

It is often very convenient, especially in single-acting engines, to drive 
the indicator directly from the main crank shaft. A device of this kind 

often found in practice but 
c ~fp\ H which does not give a true dia- 

gram is shown in Fig. 142. The 
correct method to use in this 
case is illustrated in Fig. 143, 
applying a small crank mecha- 
nism. For absolute accuracy 
the ratio of the length of this 
connecting rod ab to the length 
ao of the " equivalent crank " 
should be the same as the ratio 
of the length of the connecting 
rod of the engine is to the 
length of the engine crank. 
The eccentric device (Fig. 144) is of course the same in principle as the 
crank mechanism. The only advantage for the latter is that it can be 
conveniently adjustable for a number of engines if the eccentric E is 
made in two halves with bushings suitable for adapting it to shafts of 
different diameters. The line of greatest eccentricity must, of course, 
be set exactly parallel to the engine crank (and in the same direction). 




141. — Sliding Type of Parallel Reducing 
Motion. 



ENGINE INDICATORS AND REDUCING MOTIONS 129 



This last statement applies also to the devices shown in Figs. 142 and 

I43- 1 

Fig. 145 shows a device of the same class as the last two but suited 
only for use on large engines. It consists of an eccentric disk E, set in 



H T~1 






Fig. 142. — Inaccurate Crank Shaft Drive. 

the manner described in the last paragraphs on the crank shaft of the 
engine. A side rod T has at one end a circular roller R, and at the other 
end a finger F for the attachment of the indicator cord C. Guides G, G 




Fig. 145. — Examples of Accurate Crank Shaft Drives. 



1 The error introduced by using the plain pin device is minimized by using a wire 
instead of a string up to the point of attachment of the hook on the cord attached to 
the drum of the indicator, and making the length from the pin P (Fig. 142) to the 
guide-pulley G as long as possible. 



130 POWER PLANT TESTING 

support this rod and a spring S by its compression keeps the roller in 
contact with the eccentric. This arrangement is accurate when the 
following relations are satisfied: Let L be the stroke of the engine; M 
the length of the connecting rod; 1 the required movement of the drum 
of the indicator, ri the radius of the roller R, r 2 the radius of the eccentric 
disk E, then 

L = 1 

C r 1 + r 2 ; 

or the radius of the roller must be 

CI 

r x = r - r 2 . 

For slow-speed engines this device is generally quite satisfactory as it 
permits using a short string. The spring S must be strong enough to 



Fig. 146. — -Link and Rod on Rollers. 

overcome quickly both the frictional resistances and inertia effects of 
the reciprocating parts of the whole mechanism and the resistance of 
the springs in the drums of the indicators. 

One of the most accurate and generally satisfactory of all the types of 
reducing motions is shown in Fig. 146. It consists of a pendulum-lever 
AB pinned to a pedestal or bracket attached to the engine frame in the 
usual way. This lever has two slots, one at the bottom for a pin B 
attached to the cross-head of the engine; the other near the top is for 
the stud C attached to a light rectangular rod R supported on pulleys 
Pi and P 2 - In this way the reciprocating movement of the piston is given 
directly to the indicator drive, reducing to a minimum the error due to 
the stretching of indicator cords. This device is especially applicable 
to steam pumps (either fly-wheel or duplex types), steam-driven air com- 
pressors, tandem steam engines, etc., where there are two or more cylin- 
ders in line. 



ENGINE INDICATORS AND REDUCING MOTIONS 131 



One of these crank shaft devices must usually be applied in the case of 
single-acting engines particularly where the connecting-rod is attached 
directly to the piston. Another method often used on single-acting 
engines which do not have a closed crank case is a modification of that 
shown in Fig. 132. The stud A is supported in the usual way by a bracket 
bolted to the frame of the engine. A small fixture F (Fig. 147) provided 




Fig. 147. — Device for Single-acting Engines. 

with holes in the sides for the insertion of a small pinls attached, usually 
screwed, to the hub M of the piston. The swinging arm BH (Fig. 132) 
when pinned to the fixture F transmits freely the motion of the piston 
to the arm AB. Since both the point of attachment of the indicator 
cord and the point B move in arcs of circles about the same center A, 
the indicator drum will be moved almost in exact coincidence with the 



1 



i 



Fig. 148. — Device for Vertical Engines. 



motion of the piston. The portion of the indicator cord attached to the 
arm AB should be moved as nearly as possible parallel to the line of 
the stroke of the engine for the best accuracy. 

An indicator reducing motion suitable for use on large vertical engines 
is shown in Fig. 148. In construction it is very simple, consisting of only 
two levers. The longer one BE is supported on a pin in a bracket at- 



132 



POWER PLANT TESTING 



tached to the frame of the engine. The other lever BC is pinned to the 
cross-head at C. The indicator cord is fastened to the mechanism at E 
and should be arranged to be parallel to the line of the stroke of the engine. 
When a reducing gear of this kind is used the indicator cords would be 
very long in many cases, and a steel wire should be substituted for the 
ordinary indicator string. One end of the wire should be attached in the 
usual way at E. At the other end where it is to be hooked to the strings 
on the indicators, a small and light spiral spring should be attached by 
means of a short string. This spring when connected to some stationary 
part of the engine near the cylinder serves to keep the wire taut when 
the indicator cords are unhooked. At times when a spring is not avail- 
able a long rubber band can be substituted. 

Reducing Wheels which consist simply of a large and a small pulley 
attached to the same axis, are coming into more or less general use. A 
typical arrangement is illustrated in Fig. 149. Pulleys D and D' are 




Fig. 149. — Reducing Motion of Concentric Pulleys. 

usually connected by a sliding sleeve so that they can be disconnected 

when indicator diagrams are not being taken. 

Fig. 150 is a device for engines with long strokes. A and B are fixed 

ends of cord wrapped around a pulley D. The indicator cord g is at- 
tached to a small pulley D' and passes 
around a guide pulley G. D and D' are 
attached to the cross-head C. Then diam- 
eter D -r- diameter D' = stroke of piston -f- 
by the difference between stroke of piston 
and length of card. 

Reducing wheels are not infrequently made 
for attachment directly to the indicator, 
as illustrated in Figs. 151, 152 and 153' 
The first shows the Crosby reducing-wheel 
attachment, the second a similar device for 

the /Tabor indicator and the third an English device with three pulleys. 

These are designed for direct attachment to the drum of the indicator. 

In Figs. 151 and 152 the cord on the wheel comes from the cross- 




Fiq. 150. — Armand Stewart's 
Reducing Motion. 



ENGINE INDICATORS AND REDUCING MOTIONS 133 




Fig. 151. — Crosby Indicator and Reducing Motion Attachment. 




Fig. 152. — Reducing Motion Attachment for Tabor Indicator. 



134 



POWER PLANT TESTING 



head or from a bracket on it, and gearing drives the drum of the indicator. 
The ratio of the diameters of the wheels gives the reduction ratio. 
Each reducing wheel is provided with a " nest " of annular rings to be 
put on the small wheel to increase its diameter, so that various reduc- 
tions are easily arranged to suit the 
stroke of the engine. The device 
shown in Fig. 151 is started and 
stopped by turning the handle 14 
and moving the clutch 25. The one 
in Fig. 152 is started and stopped by 
turning the knurled nut along side of 
the wheel carrying the cord. A spring 
is located at the center of this wheel 
for bringing it back on the inward 
stroke. 
An arrangement of two indicators Ii and I 2 to be driven from a single 
reducing wheel R is shown in Fig. 154. The connection to the cross- 
head C is by a bracket B. It is best in most cases to have a reducing 
wheel for each indicator in use but this arrangement will often be very ser- 
viceable when, for example, one of the reducing wheels has broken down. 




Fig. 



153. — Three-pulley Reducing 
Device. 




Fig. 154. — ■ Single Reducing Wheel Driving Two Indicators. 

Some indicators are provided with " detents " which are devices for 
starting and stopping the drum. For stopping the drum they operate by 
engaging a pawl into teeth on the circumference of the drum near the 
bottom (see Fig. 107). Obviously the pawl must engage when the cord 
is pulled out to near the end of its stroke. After engaging the pawl the 
cord will be like y to flap about on the return stroke, catch on something, 
and be broken on the next outward stroke. The best way to prevent 



ENGINE INDICATORS AND REDUCING MOTIONS 135 

this is to connect the string to a helical spring or rubber band to keep 
it taut. 

In engine testing for long periods it is desirable to save wear of re- 
ducing wheels as much as possible by disconnecting the cord connect- 
ing the pulley with the cross-head during the 
intervals between the taking of diagrams. 
Hooks like those shown in Figs. 155 and 156 
are very convenient for this purpose, particu- 
larly if attachment can be made to pins or 
rods fastened to the cross-head. The hook 
shown in Fig. 155 is intended to be held be- 
tween the thumb and finger at about an inch 
from either end of the stroke, so that the pin Fig. 155. — Trill's Hook for 
or rod on the cross-head strikes the straight Indicator Cord, 

part of the hook, and immediately the pin or 

rod will be caught in the hook as shown by the dotted lines. The one 
shown in Fig. 156 is also frequently used. Both hooks are intended to 
be pulled off the pin or rod when the cord is to be disconnected. Un- 
less some special form of hook similar to the ones described is used it is 
difficult to connect up the cord when a diagram is to be taken. Pro- 
vision should also be made for preventing a disconnected indicator cord 
from being broken by getting tangled in the moving parts of the engine. 





•^S "-Link 

Fig. 156. — Simple Hook for Indicator Cord. 

Such difficulties can usually be avoided, and easily with such devices as 
Fig. 155 by continuing the cord from its point of attachment to the re- 
ducing motion closely past the indicator drum to a pipe or simple bracket 
that may serve, as a stationary support. Between the indicator and 
this support a spiral or helical spring of light wire or a heavy rubber 
band is inserted in the cord. By this means the cord will always be 
kept taut and in motion when disconnected from the reducing wheel 
or from the indicator, as the case may be. If a ring is attached to the 
cord close to the reducing wheel and between it and the cross-head, 
it will be continually in motion but it will be very easy to hitch into it 
the hook on the cord attached to the reducing motion. This method 
is particularly recommended in every case where wire is used instead 
of cord. 

Relative Accuracy of Indicator Motions. Pantograph types like 
Figs. 127, 130 and 137 to 139 give usually the best accuracy on small 



136 POWER PLANT TESTING 

engines, if constructed accurately and are used with short strings. The 
most important of the disadvantages is that invariably after a time 
they get shaky in one or more of the various joints, causing lost motion 
in the drive and many breakdowns in the indicator rigging. In reduc- 
ing motions like Fig. 146 such difficulties are almost entirely eliminated 
and at the same time, if the pins fit the slots nicely the movement 
is accurate. It is, however, expensive and somewhat cumbrous. 
Pendulum types, like Figs. 132 to 134, are accurate enough for most 
work. The length of the pendulum should in either type be not less 
than one and a half times the length of the stroke. Brumbo's pulley 
(Fig. 135) is shown as an example of what can be improvised with the 
assistance of a carpenter and willingness to get things done. The 
" pin and cord device " shown in Fig. 142 should be used for only very 
rough work. 

Types using concentric pulleys, like Figs. 149, 150, 151, 152, and 153, 
although suitable and quite serviceable for use on low-speed engines, 
are not accurate enough for good work on even moderately high-speed 
engines, and are always likely to make trouble on account of the indi- 
cator cords and wires getting twisted and torn. The inertia of the pul- 
leys at high speeds tends to cause them to overrun at the ends of the 
stroke. Of the last mentioned, those having no means for mechanically 
starting and stopping the motion of the drum are also objectionable 
because of the difficulty usually experienced in hooking and unhooking 
the cord. 

The crank shaft drives illustrated by Figs. 143, 144 and 145 are to be 
used only when one of the better methods is impracticable, as for ex- 
ample in the case of single-acting engines. The pendulum type shown 
by Fig. 147 can be used also on some single-acting engines and is to be 
preferred to the others mentioned. It cannot be used on types of en- 
gines having a closed crank case like some small vertical steam engines, 
most automobile engines, and two-cycle gas engines. 

All reducing motions should be designed to operate with a minimum 
number of guide pulleys. 

Errors in Indicator Diagrams and in Calculations of Indicated Horse 
Power. Taking indicator diagrams from steam or gas engines is re- 
garded by most engineers as a very simple and commonplace operation, 
and consequently it is not unusual to find inexperienced persons placing 
great reliance upon indicator diagrams and the calculations therefrom, 
when as a matter of fact the conditions under which the diagrams were 
obtained make them in error possibly from five to ten per cent. Ex- 
cept in the hands of an expert the engine indicator, even of the best 
makes, cannot be relied on to give the mean effective pressure in the 
engine cylinder with a smaller error than two or three per cent. Prin- 



ENGINE INDICATORS AND REDUCING MOTIONS 137 

cipal sources of errors found in indicator practice will be discussed in 
the following paragraphs: 

1. Errors in the Reducing Motions. The theory of the application 
of the engine indicator requires that the drum shall move in synchro- 
nism with the piston of the engine, following accurately its changing 
speed from one end of the stroke to the other. Errors in the applica- 
tion of this principle are usually found in the construction of the reduc- 
ing motion. A familiar example of such errors is shown in Fig. 142 
(see page 129) showing the drive for the drum of the indicator taken 
directly from a pin on the crank shaft of the engine. Another common 
error is in the application of parallel motion drives like Figs. 138 to 
140, when the points marked A, B and C are not in line; in other words, 
so that a straight line will not pass through the three points. Stretch in 
the string, particularly if it is long, is a fruitful source of error. If the 
string stretches only a little so that it does not bring the drum up against 
one of the stops, this error is difficult to observe; but when the cord be- 
comes so long that the diagrams drawn are not of the normal length, 
the effect can be detected by the knock of the drum against the stop 
and also by the distorted diagrams, of which Fig. 157 is an example. 
The full lines show the kind of diagrams that are obtained when the 
indicator drum strikes one of the stops. The dotted lines show the 
parts of the diagrams that are missed. 

2. Vibrations due to Inertia. Indicator diagrams often show irregu- 
lar lines due to vibrations of the mechanism of the indicator, being par- 
ticularly pronounced just after a sudden change of pressure like that 
occurring in a gas engine following the point of ignition. Fig. 158 is an 
indicator diagram taken from a gas engine which shows such oscillations. 
The same sort of effect is observed in high-speed steam engines after the 
sudden changes of pressure that occur at the points of admission and of 
cut-off. The great fluctuation of pressure at admission causes the oscil- 
lation at A in Fig. 159, while the irregularities in the expansion line at 
B follow the closing of the steam ports at cut-off. Vibration effects can 
usually be best eliminated by using a stiff er or " stronger " spring. 

It is well known that frictional resistance will dampen out vibrations. 
For this reason some engineers advise pressing the indicator pencil 
rather heavily on the drum to eliminate vibrations. This method, 
however, is not recommended, as errors due to excessive friction may be 
introduced which are far greater than those that can possibly be due to 
the oscillations shown in the diagrams. 

Attributable to vibrations will be practically only those errors resulting 
from the incorrect measurement of the areas of the diagrams. Generally 
a mean line drawn through the oscillations so that the areas of the 
loops on one side of the mean will be equal to the areas on the other 



138 



POWER PLANT TESTING 



gives the average pressure. A mean line, shown dotted in Fig. 158, 
illustrates the method. Since it is usually difficult to follow accurately 
with a planimeter lines with long oscillations it is usually desirable to 
draw the mean line in all such diagrams and follow this with the tracing- 
point of the planimeter. 





Fig. 157. 



Result of Having Indicator 
Cord too Long. 



Fig. 158. 



■ Oscillations in Diagram from 
a Gas Engine. 



3. Frictional Resistances. That serious errors in indicator diagrams 
are often caused by excessive friction has already been pointed out par- 
ticularly as regards the friction of the indicator pencil on the paper. An 
example of excessive frictional resistance in the indicator cylinder is 
shown in Fig. 160. Friction in this case was probably due to a " sticky " 
piston; that is, one that did not move freely in the cylinder of the indi- 
cator. The peculiar " step-like " appearance of the expansion and com- 
pression lines are characteristic of this fault. Irregularities in the lines 




Fig. 159. 



■Oscillations in Diagram from 
a Steam Engine. 




Fig 



— Diagram Illustrating Effect 
of a Sticky Piston. 



of diagrams due to friction cannot be corrected as accurately as can be 
done for pure oscillations; because in this case the pencil does not neces- 
sarily oscillate on the two sides of the true mean line equally, but is 
almost continually above the true mean line of pressure in an expansion 
line, and correspondingly below when drawing the mean line of com- 
pression. In the case of distortion due entirely to pencil friction the 
areas balance up fairly well, but tests show that the points in the cycle 
are late. It is therefore very important that the pressure of the pencil- 
point on the paper should be carefully adjusted by the stop-screw so 
that it makes a fine, light but clearly legible line. With some types of 



ENGINE INDICATORS AND REDUCING MOTIONS 139 

indicators specially treated 1 cards are provided on which a metallic 
pencil-point is to be used. Diagrams taken on such cards show always 
very fine and clear lines, but it is doubtful whether such diagrams are 
as accurate as those taken with a good fine black lead pencil on a card of 
ordinary paper. The reason for this criticism of the " prepared paper " 
method is that, excepting the case of the skilled operator, there is likely 
to be more friction in taking the diagram. 

4. Errors due to Faulty Indicator Connections to the Cylinder. In 
many small power plants there is only one good engine indicator. On 
this account engines fitted for only commercial indicating are usually 
provided with a three-way cock (Fig. 161) which is used to connect 
either end of the cylinder with the indicator. This arrangement of 
piping is illustrated in Fig. 135, page 126. For accurate testing, how- 




Fig. 161. — Typical Three-way Cock. 



ever, this sort of arrangement is not desirable, as the length of the pipe 
connections has an influence on the accuracy of the indicator diagrams. 
Long pipe connections have the effect of causing the indicator pressure 
to lag behind that in the cylinder, 2 and may thus give a mean effective 
pressure two or three per cent too large, depending, of course, upon the 
diameter and length of the pipe connections. Pipes which are too small 
in diameter have very much the same effect as those that are too long. 
Fig. 162 shows a distorted diagram caused by indicator connections 
that were much too long. The dotted line indicates the distorted dia- 
gram. A better arrangement is to screw an indicator cock directly into 
the end of each cylinder, and use two indicators as shown in Fig. 130, 
page 124. 

The arrangement of a three-way cock and double-pipe connections 
should never be permitted on either ammonia or air compressors because 
the clearance volume in compressors is usually reduced to the lowest 

1 An ordinarily good quality of paper can be prepared for use with brass points 
by applying to one side of the paper a thin coat of a mixture of about one part (by 
weight) of zinc oxide (ZnO), four parts of water, and one-tenth part of gum arabic. 

2 W. F. M. Goss, Transactions A.S.M.E., vol. 18 (1896). 



140 



POWER PLANT TESTING 



limit mechanically permissible, and such pipe connections would in- 
crease the percentage of clearance enormously. For use in testing com- 
pressors and very small engines the pistons of the indicators used should 
not leak much because leakage affects the degree of compression and 
leakages of ammonia fumes are most objectionable to those operating 
the plant. 

5. Lost Motion in the Piston Connections and in the Joints of the 
Pencil Mechanism. This is another fruitful source of errors. Fortu- 
nately, however, every engineer is usually able to get rid of lost motion 
due to looseness of joints without assistance. 

6. Stretching of the Cord. The effect on the diagram of the stretching 
of the cord when an engine was operating at 350 revolutions per minute 
is shown in Fig. 163. The full-line diagram was taken with a wire (no 
stretch) and the dotted line with a good quality of prepared hemp indi- 




200 Revolutions; h Cut-off 



Fig. 162. — Diagram Showing Effect of 
Long Connecting Pipes to Indicators. 




Fig. 163. — Diagram Showing Effect of 
Stretching of Indicator Cord. 



cator cord. Stretching of the cord is due mostly to friction and inertia 
of the drum 1 of the indicator. It has been shown that the mean effec- 
tive pressure is proportional to the stretching of the cord caused by drum 
friction and that the least amount of stretch in a good indicator c.ord 
is T 4_ per cen t of its length. In the case of a cord three feet long, the 
stretching under the best conditions would be about T Vo inch, making 
an error of about 5 per cent in the mean effective pressure in a diagram 
three inches long. 

Fortunately these errors due to inertia and friction have just opposite 
effects, the one making the diagram longer and the other making it 
shorter. The net result is apparently, according to reliable tests, that the 
indicated horse power even at speeds of from 300 to 400 r.p.m. is probably 
never in error more than 2 or 3 per cent if the indicator spring, drum 
spring and quality of cord are properly selected for the pressure and 
speed, assuming also that the piston and drum move freely and are well 
lubricated. 2 



1 Professor Osborne Reynolds in Proceedings Institution of Civil Engineers (London), 
vol. 83. 

2 Proceedings Inst. Mech. Engs., 1909, pages 785-798. 




ENGINE INDICATORS AND REDUCING MOTIONS 141 

Diagrams obtained with the ordinary piston and pencil indicator are 
probably as accurate as other data in engine testing if the speed does not 
exceed 300 or 350 r.p.m., but at higher speeds such diagrams are regarded 
as of little value. 1 Automobile and aeroplane engines usually operate 
at 2000 r.p.m. and over at maximum power and special indicators are 
required. The best known is the manograph or diaphragm type. An 
instrument of this kind shows practically no inertia effects and there is 
no cord used to cause errors by its stretching. Another type of optical 
indicator known as Hopkinson's is also used to some extent in England. 
It differs essentially from the manograph in having a piston instead of a 
diaphragm. It is not as easily adapt- 
able as the manograph for use on 
automobile, marine, aeroplane and 
other engines usually built with an 
enclosed crank-case as it is intended 
to be driven by connection to the 
cross-head or piston. Fig. 164. -Inaccurate Diagram Due to 

7. Throttling. Error m an mdica- i ndicator Co ck being partly Closed, 
tor diagram due to not opening the 

indicator cock completely is shown in Fig. 164. Dotted lines are due to 
this throttling in the cock. 

8. Errors in the Determination of the Scale or "Number " of Springs 
are by far the most important in indicator practice. Power plant 
engineers rely altogether too much on the calibrations made by the 
manufacturers of the indicator when it was new. That it is important to 
calibrate engine indicators with their springs frequently with some reli- 
able and standard apparatus cannot be too strongly stated. It is abso- 
lutely essential that this work should be done both before and after every 
important engine test. There are not very many indicator springs 
which after considerable use check very closely to the scales for which 
they were intended. Errors in calculations of indicated horse power 
are due more often to inaccurate springs than to any other cause. An 
engineer cannot safely assume that the true scale of the spring in his 
indicator corresponds at all accurately to the number stamped on it. 
It is not unusual to find springs in standard makes of indicators in error 
as much as four or five per cent. 

Calculations of the Indicated Horse Power of an engine show usually 

the power developed on one side of the piston, which is commonly 

stated by the formula, 

• u plan 

i.h.p. = ^ (25) 

33>ooo v oy 

1 Piston and pencil indicators are made by the H. Maihak Aktiengessellschaft which 
give accurate diagrams at from 500 to 600 r.p.m. 



142 



POWER PLANT TESTING 



Where p = mean effective pressure on the piston, pounds per square inch; 
1 = length of stroke in feet; 
a = net area of piston in square inches; 1 
n = number of revolutions per minute. 

Of the terms of this equation only one, the mean effective pressure, 
is obtained from the indicator cards. 

If we consider now only one end of the cylinder, the steam does work 
on the piston during a " forward " stroke, and, on the other hand, the 
piston does work on the steam on the " return " stroke. Hence to get 
the mean effective pressure for a stroke the average pressure during the 
return stroke must be subtracted from the average pressure on the 
" forward " stroke; and this is obviously the same as the average length 
of all the ordinates intercepted between the upper and lower lines of 
the indicator diagram multiplied by the scale of the spring. 

Usually the mean effective pressure is found by means of planimeters, 
the use of which for this purpose was explained on pages 75 to 86. An 

engineer should, however, know 
how to calculate the mean effec- 
tive pressure of an indicator di- 
agram with reasonable accuracy 
without the use of such in- 
struments. In such cases the 
method of ordinates is very con- 
venient. With suitable drafts- 
man's triangles 2 draw ordinates 
perpendicular to the atmos- 
pheric line at both ends of the 
diagram as shown in Fig. 165. 
Lay off on the edge AB of a 
piece of smooth flat paper, a scale of ten equal divisions so chosen that 
the total length of the ten divisions is a little greater than the length of 
any of the indicator diagrams. This scale should then be placed ob- 
liquely across the diagram to be measured, so that the beginning and 
end of the scale will be located on the ordinates at the ends of the dia- 
gram. Now mark the diagram opposite the divisions of the scale with 
fine points, and at the middle of each of these divisions draw ordinates 
across the breadth of the diagram. The sum of the lengths of these 

1 In all piston engines the area of the piston rod must be subtracted from the area 
of the piston on the side where the rod reduces the area effective for the action of the 
steam or other working substance. 

2 Triangles to be used for this purpose should be tested for accuracy by setting on 
a straight edge and drawing a vertical line. Then turn over the triangle and observe 
whether the line drawn coincides with the edge of the triangle. 




Fig. 165. 



Diagram illustrating Method of* 
Mean Ordinates. 



ENGINE INDICATORS AND REDUCING MOTIONS 143 

ordinates divided by ten gives the value of the mean ordinate, 1 and this 
when multiplied by the true scale of the spring gives the mean effective 
pressure. Some time can be saved in summing the ordinates if they 
are transferred with dividers one after the other to the edge of the 
strip of paper. The total length laid off divided by ten is then the 
mean ordinate. 

The Engine Constant for Indicated Horse Power. In the use of 
equation (25), page 141, where 

. , plan 

i.h.p. = - , 

33>ooo' 

considerable time can usually be saved when calculating engine tests 
if- the terms 

r^— > (26) 



called the engine constant which always remains constant for each end 
of the cylinder, are first computed carefully and then used as constants 
throughout the calculations. In other words, the indicated horse 
power is found for each end of the cylinder by taking the product of the 
terms, 

Engine Constant X p X n. 

Indicated Horse Power of Rotary Engines. Fig. 166 shows by a 
simple diagram a typical rotary engine. The steam inlet is at I and 



Fig. 166. — Diagram of Typical "Rotary" Engine. 

the exhaust is at E. A sliding blade P, corresponding to a piston, moves 
back and forth through the rotor R, as the latter revolves. In the figure 
P is shown at the point of cut-off, the dotted shading indicating the full 
charge of steam. Equation (25) can be written, 2 



pn 



33,000 



volume swept through by piston f — j-^— '■ j 



1 Methods of calculating areas of irregular figures are given on page 74. The area 
divided by the length gives the mean ordinate. 

2 In equation (25) 1 is in feet and a in square inches. The volume in cubic inches 
must therefore be divided by 12 to permit substitution in the equation. 



144 



POWER PLANT TESTING 



A hole should be tapped through the casing near the top for the attach- 
ment of an indicator to determine the mean effective pressure (p) through- 
out the cycle. This hole can also be used to determine, by filling with 
water, the maximum volume in the cycle (method explained on page 293) , 
and these data together with the number of revolutions per minute (n) 
serve "or calculating with considerable accuracy the indicated horse power. 

The steam consumption per i.h.p. per hour for all types of such engines, 
if well made and when new, is about 100 to 125 pounds. It is difficult to 
take up wear in such engines, so that after use for a short time much steam 
leaks through without doing work. 

Speed Counters. Some kind of mechanical counter is ordinarily used 
for determining the speed of engines and of other machinery with re- 
volving shafts. For the usual services in testing, a hand speed counter 




Fig. 169. — Starrett's Differential Speed Counter. 

(Fig. 1 69) is considered most reliable. 1 It is generally applicable, inex- 
pensive, and accurate, so that every engineer should have one. 

For slow-speed engines some type of fixed counter (Fig. 170) is fre- 




Fig. 170. — Integrating Engine Counter. 

quently provided for attachment to the gage board in the engine-room. 
For gas engines operating by a " hit and miss " method of governing 
such fixed integrating counters are used in many places for counting the 

1 Starrett's hand counters are generally preferred both in America and abroad. 



ENGINE INDICATORS AND REDUCING MOTIONS 145 

number of explosions. Actually the number of times the gas valve opens 
is counted. The greatest trouble with counters of this type is that they 
will sometimes " stick " even at the normal 
speeds of stationary engines. 

Schaeffer & Budenburg make a pointer and 
dial revolution counter (Fig. 171) which is 
suitable for observing high speeds. 

Tachometers, operated centrifugally (Figs. 
172 and 173) or by the vibrating reed method 
(Figs. 174 and 175) are not accurate enough 
for the determination of indicated or brake 
horse power. They can be used conveniently, 
however, for observing roughly variations in 
the speed of steam turbines or electric generators when no accurate 
results are to be calculated from the observations. The vibrating reed 
type operates by being placed on the frame of the machine and the reed 




Fig. 171. 



- Belt-driven Speed 
Counter. 




"G^ 




Fig. 172. — Hand Type of Centrifugal 
Tachometer. 



Fig. 173. — Sleeve and Weights 
in Centrifugal Tachometers. 



which is most nearly in synchronism with the vibration of the machine 
indicates by its excessive vibration the speed on a calibrated scale. 
Belted tachometers because of the added uncertainty regarding the slip 
of the belt are particularly unreliable. 




Fig. 174. — Details of Vibrating Reed Tachometer. 

Electro-magnetic tachometers depend for their operation on the inten- 
sity of the magnetic drag due to flux generated which is proportional to 
the speed. They are simple in construction, but rather delicate for 
commercial service and the temperature correction is usually difficult 
to compensate. 



146 



POWER PLANT TESTING 



Fluid tachometers are essentially small centrifugal pumps discharging 
a colored liquid (usually alcohol colored red) into a vertical glass dis- 
charge pipe. The blades of the wheel are radial so that the instrument 
registers the same when running in either direction. The greater the 
speed the higher the liquid will stand in the tube. Since the height to 




Fig. 175. — Commercial Form of Vibrating Reed Tachometer. 



which the liquid will be forced in the tube varies approximately as the 
square of the speed of the wheel, the upper part of these tubes has a very 
much more open scale than near the bottom where accurate observations 
are difficult. Speeds less than 300 or 400 r.p.m. cannot be satisfactorily 
observed with such instruments. 



CHAPTER VI 

MEASUREMENT OF POWER — DYNAMOMETERS 

A dynamometer, according to its derivation, is an instrument for 
measuring force or " power." These are of two kinds: 

1. Those absorbing the power by friction and dissipating it as heat. 

2. Those transmitting or passing on the power they measure, thus 
wasting only a small part in friction. 

Absorption Dynamometers (Prony Brakes). Of the class of dyna- 
mometers in which the power received is all absorbed in friction, the 
type generally used is called a Prony brake, named for Rev. John Prony, 
who many years ago developed a device of this kind for measuring 
power. 1 One of the simplest forms is shown in Fig. 180. 

It consists of a lever A, from which a weight w is suspended from one 
end, and a block B, supported on a revolving drum or pulley, is at- 
tached to the other end. A strap to which wooden cleats are fastened 
is held in place and tightened by the thumb-nuts N, N. When the 
friction on the strap and block just balances the weight w, the lever 
arm A is horizontal and the apparatus is in adjustment. Stops, marked 
S S, are provided so as to limit the movement of the lever arm. 

When the brake is adjusted or " balanced," the work done in a given 
time in producing the friction (the power absorbed) is measured by the 
weight moved multiplied by the distance it would pass through in that 
time if free to move. Then if, 

r = length of brake arm in feet. 2 

n = revolutions of the shaft per minute. 

w = weight on the brake arm in pounds. • 

Brake Horse Power (b.h.p.) =— .27) 

1 Strictly speaking, a brake of this kind does not provide means for directly measur- 
ing power, as, for example, horse power, because the element of time is not indicated. 
In other words, it measures the tangential force, of which a couple (torque) in linear- 
weight units, such as foot-pounds, can be computed. 

2 The length of the brake arm is measured by the perpendicular distance from the 
line of action of the weight w to the center of the wheel. When the arm A is horizontal, 
as in Fig. 180, the length of the brake arm is usually measured by the horizontal dis- 
tance from P to a line passing through the center of rotation perpendicular to the arm. 

147 



148 



POWER PLANT TESTING 



In equation (27) the fraction 



is a constant quantity for a given 



33,ooo 

brake and is called the brake constant. When a brake like the one in 
Fig. 180 is used the effective weight of the brake itself as weighed at the 
point P must be added to the weight w. 

According to Bach suitable dimensions for a brake of this type are 

given by bd = ■ * ■- where d is the diameter of the brake pulley in 

inches, b is the breadth of the brake blocks in inches (usually about 1.5 
times the diameter of the shaft), b.h.p. is the brake horse power to be 
absorbed, k is § for air cooling, and varies from 2.5 to 5 for water cool- 
ing as the speed increases. 1 




Steel Band 



Fig. 180. — Simple Prony Brake. 



A very common variation of the Prony brake is illustrated in Fig. 181. 
The block B in the preceding figure is replaced by a series of narrow 
cleats of maple or oak. 

Rotation being in the opposite direction from that in Fig. 180, the 
knife-edge at E on the arm A will now press on the pedestal T, and the 
weight w can be determined by weighing the pressure on a platform- 
scales S. Since the scales receive not only the pressure due to the force 
producing friction, but also that due to the weights of the brake and of 
the pedestal, these weights must be determined and are to be subtracted 
from all of the readings of the scales to obtain the net weight w for sub- 
stitution in equation (27). Weight of the brake and the pedestal, called 
the, zero reading, must be obtained with the brake strap slack, so that 
the block B will rest as lightly as possible on the pulley. With small 
engines this zero reading is obtained most accurately by observing the 
weights on the scales when the brake pulley is turned around by hand 
first in one direction and then in the other. In this way we obtain for 
both the brake and pedestal, with rotation in one direction the weight 
plus the friction due to their own weight, and with rotation in the other 
direction the same weight minus the same friction. Half the sum of 

1 For information regarding the designing of Prony brakes for absorbing large 
powers the reader is referred to Engine and Boiler Trials, by R. H. Thurston, pages 
260-279. 



MEASUREMENT OF POWER — DYNAMOMETERS 149 



the two readings is, therefore, the weight corresponding to the pressure 
on the scales due to gravity alone. With large engines it is sometimes 
difficult to turn them uniformly by hand, so that the zero reading 
must be obtained by some other method. This is done usually in 
practice by placing a very small rod on D (Figs. 180 and 181) ver- 




=^ 



I 



Fig. 181. — Prony Brake with Platform Scales. 

tically over the center of the shaft. Then if the strap is loose and 
due care is observed, the pressure on the scales can be obtained with 
sufficient accuracy without rotation. The cleats are attached to the 
bands by wood screws inserted from the outside and countersunk into 
the bands. Screws used for attaching the cleats to the upper block are 
inserted through the cleats and countersunk into the wood. At least \ 




"Rough and Ready" Prony Brake. 



inch spaces should be left between the cleats to permit air circulation. 
In all such constructions for dynamometers screws and nails should not 
touch the rubbing surface as they are likely to cause the friction to be 
variable and the sound produced is objectionable. Many designers 
cut grooves into the inside surface of a few of the cleats. These grooves 
are to be filled with thick grease for lubrication. 

A similar arrangement to Fig. 181 is shown in Fig. 182, showing maple 



150 



POWER PLANT TESTING 




Fig. 183 



cleats screwed to a leather belt. A piece of old belting is ordinarily used 
for this purpose so that by this method a very inexpensive Prony brake 

can be made quickly in any power 
plant. It has also the important 
advantage over the two preceding 
types in that it is readily adjust- 
able to different sizes of pulleys. 
Washers should be provided for 
the heads of the screws used to 
attach the cleats to the belt. If 
the inside surface of the pulley can 
be satisfactorily cooled by water 
the rubbing surface of the cleats 
need be not more than five square 
inches per brake horse power at 
peripheral velocities not over 2,000 
feet per minute. For a velocity 
of 5,000 feet per minute about 10 
square inches per brake horse power 
should be allowed. 
Another form of Prony brake is illustrated in Fig. 183, called a strap 
brake. 

It is made up merely of a band of steel or leather or of strands of rope 
placed over or wrapped around a suitable pulley. 1 In this case weights 
must be suspended from both sides of the brake wheel or pulley. 

In the case of the strap brake, Fig. 183, the net pull, corresponding to 
the weight w, in equation (27), page 147, is Wi — w 2 . Now the same 
relation would hold if, as is often done, a spring balance is fastened to 
the floor on say the left-hand side; the pull registered by the spring 
balance would then be W1, 2 and the net pull is, as before, Wi — w 2 . 

1 It is desirable to use for Pony brakes pulleys of which the section of the face is a 
double " U," like Fig. 184. The outside rims are for keeping the brake in position on 
the pulley and those on the inside for receiving a small stream of water played upon 
the inside of the pulley. This stream of water by its evaporation will assist materially 
to dissipate the heat generated. Such brakes are often operated with pipes arranged 
to discharge water into the pulley and another pipe to carry it away. This is an ex- 
cellent system provided the latter pipe is used only to carry away a little overflow, but 
if so much water is used that there is practically no " steaming," the inside rim of the 
pulley will fill up with water to be spattered around in every direction as well as over 
the face of the pulley, where it is particularly objectionable, as it produces variable 
friction. 

2 To the pull (wi) must be added, however, the weight of any hooks placed be- 
tween the end of the strap or rope and the spring balance; and if the balance is for any 
reason suspended in the inverted Dosition the weight of the balance itself must also 
be added. 



MEASUREMENT OF POWER — DYNAMOMETERS 151 



Brake horse power is calculated then by equation (27), substituting for 
w the net pull Wi — w 2 , so that 

2 7rrn (wi — w 2 ) 



(b.h.p.) 



(28) 



33,000 

where r is the radius of the pulley plus half the thickness of the strap, in 
feet, and n is the number of revolutions per minute. This type of strap 
brake is very accurate and sensitive, but is suitable only for low powers. 
About the same friction surface must be allowed as for wooden blocks in 
Bach's formula. 



I : 




Fig. 184. — Special Pulley for Brakes. 

Rope brakes, 1 like the one shown in Fig. 185, are much used for " com- 
mercial testing " of engines, as they are easily portable or can be made 
quickly at a small expense from materials always at hand. Moreover, 
they are self-adjusting, so that accurate fitting is not required. One of 
this type consists of a rope doubled around a pulley or fly-wheel on the 
shaft transmitting the power to be measured. 

As the friction at the rim of the pulley increases, the tendency will be 
to lift up the weight Wi. The effect will be to reduce the tension in the 
end of the rope overhead connected to the spring balance and thus 
prevent a tendency to further increase of the friction. Several U-shaped 
distance pieces of wood, preferably maple, are provided to prevent the 
rope from slipping off the pulley and to keep the parts of the rope sepa- 
rated. These distance pieces should be attached to the rope by soft 
iron or copper belt lacing, drawn in from the outside of the wooden pieces 

1 Sir William Thomson (Lord Kelvin) invented in 1872 the first rope brake of which 
we have any record. Although he utilized this device as a friction brake, it was not 
used by him as a dynamometer. 



152 



POWER PLANT TESTING 



through the center of the rope, instead of being fastened with screws or 
nails on the inside, which will heat to a high temperature and then char 
the rope. Sometimes such fastenings when of hard metal will cut 
grooves into the surface of the pulley. In this arrangement the spring 
balance must be supported from some point overhead. 

An anchoring rope or safety stop securely attached to the weight w x 
should be provided to prevent the weights going over the wrong way 




Fig. 185. — Rope Brake. 

when starting or stopping an engine in case the valve is not very well 
set. Its weight or the weight of that part suspended from the weights 
must be included in Wi. Similarly the weight of the rope between the 
spring balance and the point where it touches the pulley should be de- 
ducted from the readings of the spring balance in accurate work. Spring 
balances require frequent and very careful calibrations. A modifica- 
cation of practically the same rope brake is shown in Fig. 186, where 
the rope is fastened at the top and bottom to a frame resting on a plat- 
form scales. 



MEASUREMENT OF POWER — DYNAMOMETERS 153 



Equation (28) is used also for calculating the brake horse power 
for a rope brake, except that r becomes the radius of the pulley or brake 
wheel plus half the diameter of the rope. All in feet. 

Rope brakes are best arranged with the rope placed on the pulley 
double as in the figures so as to form a loop for supporting the weights. 
A brake made in this way of double f-inch rope and provided with six 
cleats each of about ten square inches of rubbing surface will absorb 
fifty horse power if the pulley carrying the brake is about three feet in 
diameter, and the speed is not over 300 revolutions per minute. For 
absorbing smaller powers half-inch rope with 4 cleats can be used. 




Fig. 186. — Rope Brake with Standard. 

Manilla or cotton rope is generally preferred. By steeping the rope in 
a mixture of deflocculated graphite and melted tallow its frictional prop- 
erties are improved. 

Water- jacketed Bands. A very good method of putting a brake on 
a wide wooden pulley is shown in Fig. 187. Outside of the steel band is a 
similar band of rubber and canvas. Canvas and steel bands are riveted 
along the edges, making the space between the canvas and steel a water- 
tight compartment. Connections are made with the water supply and 
drain at the ends of the brake strap by means of flexible hose, and a cur- 
rent of water is kept circulating round the wheel, quickly removing the 
heat generated by friction. 

The brake strap may be of almost any width, 20 inches being that 
used by Professor Goss. The face of the pulley must be cylindrical 
and not rounded, and any inequalities in the face should be made good 



154 



POWER PLANT TESTING 



before proceeding to use it. Especially is this the case at the joint in 
split pulleys, and if any space between the halves is left at all, this 
should be filled with glued wooden plugs. The thickness of a steel band 
used on a pulley 24 inches in diameter was No. 12 gage. A layer of rub- 
ber should be inserted at the joints between the canvas and steel band, 
so as to ensure a good joint, and special cast-iron ends are usually riv- 
eted to the brakestrap and fitted with water connections. 




Fig. 187. — Water-jacketed Band for Brake. 

A somewhat similar brake has been used at the Pennsylvania State 
College, consisting of a flat strap with both sides made of copper. It is 
applied to the fly-wheel, much in the same manner as the Prony brake. 
The ends are coupled together by an adjustable screw. The pressure of 
the brake strap on the wheel is produced and regulated by water flowing 
through the tube, much in the same way as in the Alden dynamometer 
(page 155). If the wheel surface is maintained in a well-lubricated con- 
dition, the wear of the copper tube is inappreciable. In a modified form 
of this brake a thin metallic band is interposed between the copper tube 
and the wheel, and consequently no wear of the tube takes place. 

Fan Brakes or Dynamometers. For determining the power of high- 
speed engines a dynamometer consisting of two flat fan blades arranged 




Fig. 188. —Fan Brake. 

to be attached to the engine shaft is very convenient. Power is ab- 
sorbed by the " fan " action of the plates on the surrounding air. 



MEASUREMENT OF POWER — DYNAMOMETERS 155 



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Amount of power absorbed by fan blades depends (1) on the size of the 
blades, (2) their distance from the center of rotation, and (3) on ap- 
proximately the cube of the number of revolutions per minute. Fig. 
1 88 shows a somewhat elaborate testing-base for automobile and 
marine engines. The engine is connected by means of a universal 
coupling C to the shaft S to which the fan blades E are attached. The 
frame Q is for supporting the engine. A tachometer J is used to indi- 
cate the approximate speed. The fan is shown enclosed in a glass 
frame-work M to prevent the air currents from other engines, etc., from 
interference with the discharge of air from the fan blades. Fig. 189 
shows typical calibration curves for the fan in Fig. 188. Fans for this 
purpose are usually calibrated by at- 
taching them to a variable-speed elec- 
tric motor of which the efficiency curve 
is known. For appropriate work a fan 
built as shown in the figure can be 
used for testing and even without the 
casing M the curves will show satis- 
factory values of power with a prob- 
able error of less than three per cent. 
The blades are ten inches wide in the 
radial direction, fourteen inches wide 
in the axial direction, and § inch thick. 
Numbers on the curves indicate inches 
from the center of the shaft to the middle of the blades. This distance 
can be varied by shifting the bolts. The speed to be used in accurate 
calculations should be taken on a high-speed engine with a good hand- 
counter. 

Alden Brake. An entirely different type of absorption dynamometer 
is the Alden brake, illustrated in Fig. 190. 

In this apparatus the rubbing surfaces producing the friction neces- 
sary for absorbing the power are separated by a film of oil, and the 
heat generated is carried off by a stream of water circulating as indi- 
cated by arrows. It consists of a disk of cast iron A, which is connected 
to the shaft S, transmitting the power. This disk revolves between two 
thin copper plates E, E, fastened together at their outer edges to form 
a shallow cylinder which is filled with a bath of heavy (cylinder) oil. 
Water under pressure is discharged into the chamber adjoining the 
copper plates and any increase in pressure causes the copper plates to 
press toward the cast-iron plate A with more force. The friction of the 
thin film of oil between these copper and iron plates tends to turn those 
of copper, but as they are rigidly connected to the outside casing C 
carrying the brake arm P, the tendency to turn can be determined by 



2C0 400 000 800 1000 1200 1400 1000 1S00 
Kesulting Curves from on Actual Calibration of a Fan Dynamometer 

Fig. 189. — Curves for Fan "Brake in 
Fig. 188, with 10" X 14" Blades. 



156 



POWER PLANT TESTING 



weighing as with a Prony brake. To maintain the moment of resistance 
constant under all circumstances the pressure and consequently the flow 
of water into the casing is automatically regulated by a cylindrical valve 
V, which becomes partially closed if the brake arm moves above a 
certain horizontal position. This valve is shown in section in Fig. 191. 
The end at W is connected to the water main and the other end Y to the 
brake casing by means of a right-angled bend R (Fig. 190). Water enter- 
ing by the pipe W passes through the ports N and then through the 
ports H into the pipe Y. Now a small angular movement of the pipe 




Fig. 190. — Alden Brake. 

W, relative to the pipe Y, will open or close the ports H and thus reg- 
ulate the supply of water. These ports are very narrow, so that a 
very small angular motion is sufficient to close them. By making the 
outer casing of the valve of rubber it is found to be sufficiently flexible 
to permit moving the valves and at the same time it offers very little 
resistance to the movement of the casing. 

Reynolds-Froude Dynamometer. Professor Osborn Reynolds has 
designed a modification of the Froude brake which is shown in section 
in Figs. 192 and 193. This device has a very large capacity for absorb- 
ing power. One of these brakes with a single rotor only 30 inches in 
diameter will absorb 700 horse power at 200 revolutions per minute. 



MEASUREMENT OF POWER— DYNAMOMETERS 157 





Fig. 191. — Regulating Valve in Alden Brake. 




M 





L 




;x /yi 




£# 


^ tkUQ- j 


i ^ 




^yZy 






?h5 






i 


T i 


b^ 


n 


vj 



Fig. 192. — Reynolds-Froude Dynamometer. 



" M 
Fig. 193. — Reynolds-Froude 
Dynamometer Shown Dia- 
grammatically. 



Water is supplied to the apparatus through the flexible pipe marked 
E (a rubber hose is very satisfactory) from which it passes in the direction 
of the arrows into the space H, (Fig. 193), then into the centers of 
the vortices through the holes J (shown dotted) which are drilled 



158 



POWER PLANT TESTING 



through the walls of the pockets. From these pockets the water passes 
between the rotor and the casing into the space M from which it dis- 
charges through the discharge outlet D into the drain. 

If any air collects in the center of the vortices it can escape through 
the holes I in the pocket walls in the casing into the cored channel L and 
the air outlet pipe O. If any water comes through these passages with 
the air it is carried off through a funnel and pipe emptying into the main 
discharge pipe D. The brake horse power (b.h.p.) for this dynamometer 
is expressed on a very conservative rating by the equation 



b.h.p. 



To^ n2dD > 



where n is the number of revolutions per minute and d is the diameter 
of the rotor in inches. 

Water Brakes. Power can also be absorbed by moving in water a 
rotor similar to those in steam turbines. Such an apparatus is called 
a turbine water brake. A good example is shown in Figs. 194 and 195. 




Fig. 194. — Westinghouse Water Brake. 



It is the type used by the Westinghouse Machine Company of Pitts- 
burg for testing the power of large steam turbines. It consists of a rotor 
R, mounted on a shaft S, S, of which one end is arranged to be connected 
directly by means of a coupling to the shaft of the turbine or engine to 
be tested. This rotor revolves within a closed casing Z, supported on 
the journals J, J, through which the shaft passes. Around the periphery 
of the rotor there is a series of rows of vanes which when revolving tend 



MEASUREMENT OF POWER — DYNAMOMETERS 159 

to give to any water contained in the casing a rotary motion. Between 
every two rows of vanes on the rotor there is fitted a row of stationary 
vanes attached to the inside of the casing. This arrangement is illus- 
trated diagrammatically in Fig. 195, where the cross-hatched sections 
represent the stationary vanes and the " solid " sections the moving vanes. 
The tendency of the moving vanes to produce this rotary motion of the 
water is, as it were, resisted by the stationary ones, and this action 
develops a very large amount of heating, due to fluid friction in a manner 
analogous to the operation of a Prony brake or any other absorption 
dynamometer. As a result of this friction a force is developed tending 
to turn the casing in the direction of motion of the rotor. The casing, 
however, is prevented from turning by a radial arm bearing down on a 
platform scales. The intensity of this tendency to turn can be regulated 
as in the Alden brake (page 155) by adjusting the valves controlling the 
flow of water through the casing. The vanes on the rotor are of the 




8-3 



fT eaa ^ eza VT era fZ 



r w r 



$k~-%;-WM-fc ■% fc £ £ 

^.m^ n c £ - £ 



Fig. 195. — Vanes of Westinghouse Water Brake. 



same kind as used in steam turbines and have the function of imparting 
a high velocity to the water flowing through them in an axial direction. 
Water enters the casing through the inlet pipes C, C (Fig. 194), discharg- 
ing a stream from both sides of the casing toward the central portion of 
the rotor. At the middle of the periphery of the rotor there are a number 
of slots or ports A, A, A, A through which the water discharges to the 
right and left, passing first through a broad central row of stationary 
vanes shown in Fig. 195. Escaping from these vanes it is picked up by 
the rows of moving vanes on each side, which give it a high velocity and, 
in turn, discharge it into the adjacent rows of stationary vanes where the 
velocity just acquired is checked, and so on across the face of the rotor, 
the moving vanes adding velocity only to be lost in the next row of sta- 
tionary vanes. From the last rows of moving vanes the water is dis- 
charged into semicircular passages B, B', which direct the flow of water 
into the center of the rotor when the cycle is repeated. The water brake 
illustrated here was designed for high powers, so that a number of rows 
of vanes was necessary. For small powers of, for example, from 200 to 



160 



POWER PLANT TESTING 




Fig. 



d d 

196. — Simple Water Brake. 



500 horse power, not more than two rows of moving vanes with the 
corresponding number of stationary vanes would be required. 1 

Power absorbed by a water brake is calculated in the same way as for 
an ordinary Prony or rope brake. 

In the operation of the brake the water is quickly raised to the boiling- 
point and a considerable portion evaporates, carrying off as steam very 
large quantities of heat. Vents for the escape of this steam are indi- 
cated by D and D' in the fig- 
ure, showing the cross-section 
of the brake. Unless consid- 
erably more water, however, 
was admitted to the casing 
than was required to replace 
that lost by evaporation, the 
action of the brake would be 
more or less irregular, so that 
an excess of water is supplied 
and there is a constant dis- 
charge of hot water through 
the passages marked E and E'. 
Another type of water brake is shown in Figs. 196 and 197 which is 
also used for testing engines and turbines. 2 The revolving paddle wheel 
or " runner " R is designed to run in very close clearance with the 
serrated rim piece P. The 
outer casing is rigidly attached 
to the lever arm A made of 
such a length as to facilitate 
rapid calculation. A little 
roller or wheel W on the end of 
this arm rests upon the plat- 
form scales used to weigh the 
load. 

Water is admitted through 
a flexible hose connection at 
the opening I and from there 
enters the interior of the wheel. 
When the wheel is revolving 
this water is thrown out by centrifugal force through small holes drilled 
in the rim, entering into the outer teeth spaces. In this passage of the 

1 To calculate the resistance of such vanes see " The Steam Turbine," by the author, 
pages 115-125. 

2 A very satisfactory water brake is also made by the Michigan Motor Specialties 
Co., Woodbridge Street, Detroit. It has an extensive sale for automobile testing. 




Fi<; 



Section of Brake shown in Fig. 196. 



MEASUREMENT OF POWER — DYNAMOMETERS 161 



water a considerable fluid resistance is produced. The water finally es- 
capes after passing through this tortuous passage through the close clear- 
ance around the outside of the wheel and discharges through the pipes 
connected at D. 

Webb's " Viscous" Dynamometer, Fig. 198, consists of a number of 
flat steel plates Pi (circular saw blanks are excellent) fastened to a hub 
H which is keyed to the driving shaft 
S. Between these plates on the shaft 
are other plates P 2 rigidly attached to 
the casing C. When a liquid is put 
into the casing the rotating plates Pi 
tend to carry it around with them by 
the action of viscosity, and the turn- 
ing moment of the shaft S is commu- 
nicated to the fixed plates P 2 and to 
the casing. The casing is supported 
on pedestals E provided with ball- 
bearings. The turning moment on 
the casing is balanced by weights 
placed on a horizontal arm as ar- 
ranged for the Alden dynamometer 
(Fig. 190) or may be set up so as to 
press on a platform scale as in Fig. 
181. The latter method is probably 
the better. Water is most commonly 
used as the liquid. It enters through 
the funnel F near the center of the 

casing and leaves at the discharge pipe D. A flow of liquid is maintained 
which carries away the heat generated. The power absorbed varies as 
the cube of the speed and the fifth power of the diameter. The frictional 
or " viscous " resistance can therefore be varied by adjusting the depth 
of the water in the casing. Usually a number of holes are made in 
both sets of plates through which water can pass to the discharge con- 
nection without having the casing filled to the tips of the fixed disks 
before overflowing to the next compartment. The quantity of water 
in the casing can be regulated by both the inlet and discharge valves. 
It is generally best to adjust both valves at the same time for large 
variations in load. Viscosity of the water decreases somewhat with 
rise of temperature of the water. 

Professor Webb has also arranged in some of his designs to supply 
the water through a hollow shaft and regulate the supply by a piston 
valve to be adjusted axially to supply a varying number of compart- 
ments. 




Fig. 198. 



Webb's "Viscous" Dyna- 
mometer. 



162 



POWER PLANT TESTING 



Regulation is accomplished not only by varying the radial depth of 
the water but also by changing the number of compartments containing 
water. In this latter arrangement no holes are required in the fixed or 
stationary plates to permit draining. Discharge connections are pro- 
vided for each compartment so that there are as many drain pipes as 
compartments. 

The dynamometer starts easily and without load so that it is better 
suited for use on steam turbines than those of the Alden and Froude 
types. The steel plates are the only parts subjected to high centrifugal 
stress and they are strong enough for all practicable speeds. 

This apparatus is not large for the power absorbed. One of these 
dynamometers provided with two disks, each two feet in diameter, 
absorbed 180 brake horse power when running at 2500 revolutions per 
minute with a radial depth of three inches of water, and with one inch of 
radial depth of water 60 horse power can be absorbed. Brake horse 
power (b.h.p.) absorbed by each rotating plate is approximately 



b.h.p. 



n 3 (r 2 5 - ri 5 ) 
130,000,000 



where n is the revolutions per minute, r 2 is the radius of the moving 

plate in feet and r x is the inner radius of the annular ring of water in the 

casing. 

Dynamos (Electric Generators and Motors) as Power Dynamometers. 

One of the most convenient means for measuring the power of high- 
speed engines and turbines is to con- 
nect an electric generator to the main 
shaft as in Fig. 199. Then if the effi- 
ciency of the generator is known at 
the particular speed and output at 
which it is to be operated, a very ac- 
curate method of measuring the power 
of the engine or of any other type of 
motor becomes readily available. The 
output of the generator should be de- 
termined by observations of the volts 
and amperes with carefully calibrated 
portable instruments. Remembering 

that for direct-current generators volts times amperes gives watts and 

that 746 watts are equivalent to one horse power, then if e.h.p. is the 

horsepower output of the generator we have 




^ 



Fig. 199. — Electric Generator used as 
Power Dynamometer. 



e.h.p. 



volts X amperes 
746 



MEASUREMENT OF POWER — DYNAMOMETERS 163 

It is not unusual to hear this result called the " Electrical " horse power 
of the engine or turbine. 1 

The actual horse power delivered to the generator is, of course, the 
brake horse power, and into this result the efficiency of the generator 
enters. Thus, for direct- (or continuous) current generators 

, volts X amperes 

* p ' 746 X efficiency of generator * 

The load on the generator should be maintained uniform by absorb- 
ing the electrical output in lamp or wire resistances for small powers 
but for larger powers a water resistance or rheostat is generally used. 
Electrodes are generally made of \- to ^-inch iron or steel plates, allow- 
ing about 1 square inch per ampere. 

As a rule electric motors are very serviceable in mechanical engineer- 
ing laboratories as power dynamometers. The efficiency is easily ob- 
tained, the usual method being to determine an efficiency curve for 
varying power inputs by a Prony brake test. This efficiency is 

Efficiency of motor = ' , 
e.h.p. 

where e.h.p. is the " electrical " horse power input, as measured with 
voltmeters and ammeters. 

If then a pump, air compressor, ventilating fan or a similar machine 
is to be tested by the electrical method, it should be direct-connected to 
the shaft of the motor, and its efficiency E will be 

u.h.p. 



E = 



e.h.p. X efficiency of motor' 



where u.h.p. is the useful work done by the machine, in horse power. 

This last method serves also as a convenient method for obtaining 
the efficiency of generators, since by connecting it directly to the shaft 
of a motor previously " calibrated " (for efficiency) the electrical out- 
put of the generator and the input to the motor are readily deter- 
mined. 

When a so-called variable-speed motor is used as a dynamometer, its 
efficiency must be determined at the particular speed and power at 
which it will operate when driving the machine to be tested. 

Eddy-current Brakes 2 are built with a number of electro-magnets and 
one or more copper disks. Either the coils or the copper disks may be 

1 When an alternating-current generator is used the power factor must also be 
measured with a suitable instrument. In this case, the actual e.h.p. is (volts X 
amperes X power factor) -5- 746. 

2 For more information regarding the design of this type see "Eddy-current Brakes" 
in Journ. Inst. E. E., (London) vol. 35, (1904-5). 



164 



POWER PLANT TESTING 




rotated with the shaft while the other is held stationary. Eddy cur- 
rents generated by rotation with the electro-magnets excited produce a 
resistance of which the moment is measured by a lever arm and scales 
as with similar forms of dynamometers. 

Transmission Dynamometers. Instruments of this type are used to 
measure the amount of power transmitted without absorbing any more 
power than is absolutely needed to move the dynamometer. 

Goss Belt Dynamometer. One of the simplest forms of transmission 
dynamometers, designed by Professor W. F. M. Goss, is illustrated in 

Fig. 200 by a line drawing. Being so 
simple in construction, it can readily 
be made in any factory or workshop 
with the materials available. It is 
essentially a differential lever measur- 
ing the difference in tension between 
the two sides of a belt. This lever is 
pivoted at the point D and to it are 
attached the shafts carrying the pul- 
leys A and B. Weight hangers are at- 
tached to the ends of the beam. The 
beam and hanger must be balanced to 
be in the horizontal position, that is, 
in the position of equilibrium when 
the belt is not moving. Power trans- 
mitted is measured by the product of 
the speed of the belt and the differ- 
ence in belt tension between the two 
sides of the dynamometer. 

The force tending to raise the left- 
hand end of the lever is to be twice 
the tension ti of the tight side of the belt, while that raising the right- 
hand side is twice the tension t 2 in the slack side of the belt. These 
tensions on the two sides of the lever can be measured by weights Wi and 
w 2 suspended from the hangers. The force tending to rotate the lever 
is therefore twice the difference in tension on the two sides of the belt 
2 (ti — t 2 ) and this force acts with a leverage AD = DB = r, when these 
two arms are made equal. If now the distance from the pivot D to the 
point of support of the weight Wi is made twice AD = 2 r, and if the 
weight Wi is made equal to the difference in the tensions it will balance 
the lever. For these conditions, taking moments about D, 
Wi X 2 r — 2 tir + 2 t 2 r = o, 

2 Wi = 2 (ti — t 2 ), 
Wi = ti - t 2 . 



2ji 



^ 



Fig. 200. — Goss Belt Dynamometer. 



MEASUREMENT OF POWER — DYNAMOMETERS 165 

Now in any transmission system the difference in the tension of a belt or 
a rope on the two sides of a driven pulley multiplied by its speed is a 
measure of its power. If, then, d is the diameter of the driven pulley C, 
plus the thickness of the belt or rope in feet, n is the number of revolutions 
per minute of this pulley, and Wi is the weight in pounds on the left-hand 
side required to balance the lever; when power is transmitted, then, 

Horse power transmitted = l (20) 

33,ooo 

To reduce the vibrations of the apparatus a dash-pot is connected to 
the right-hand side. To prevent excessive movement of the lever when 
unbalanced, stops are placed above and below the lever on the left- 
jiand side. 

Another form much used for mill purposes and fan testing is the belt 
dynamometer, shown in Fig. 201. The driving pulley is A and the driven 
pulley is B. The connecting belt passes over the pulleys C and D. 




Fig. 201. — Compact Belt Dynamometer. 

These two pulleys are mounted on the frame of the dynamometer carry- 
ing a scale beam A, all of which turns on the center of support. The dif- 
ference in the total stress on the two sides of the belt is computed by multi- 
plying the net weight on the beam by the equivalent leverage, the latter 
being found by dividing the length of the beam by the distance from the 
center of support to the centers of pulleys C or D. 

Differential Dynamometers. The apparatus illustrated in Fig. 202 
is typical of a number of dynamometers indicating by means of a differ- 
ential lever operated by gearing, the amount of power transmitted. 1 
This is a very common form of transmission dynamometer. Power is 
received from the motor (or engine) by the shaft A, which is connected 
only indirectly by means of gears to the shaft A' opposite, which trans- 
mits the power to the work. To the adjoining ends of these shafts bevel 
wheels B and D are attached. The lever L turns on an axis concentric 
with the shafts A and A', in a plane perpendicular to them. It carries 

1 Similar forms of differential dynamometers are known as White's, King's and 
Bachelder's. The first instrument of this kind, it is stated, was invented by Samuel 
White in 1780. These dynamometers are sometimes called epicyclic, signifying "wheels 
traveling around a circle or around another wheel." 



166 



POWER PLANT TESTING 



bevel wheels C and Ci, gearing with B and D, through which the power 
is transmitted. There is a tendency then for the left-hand end of L to 
go downward and for the right-hand end to rise. If, furthermore, the 
lever L were permitted to revolve, no work would be transmitted from 
B to D, and therefore D would remain stationary. As these gears are 
usually proportioned so that B revolves with half as many revolutions 
in a given time as L, a force applied at B at a given radius from the center 
will balance a weight twice as large at the same radius on the lever L. 



Weight 




Shaft to Work. 



Fig. 202. — Typical Differential Lever Dynamometer. 

Then the moment of the force applied to the lever L to balance it must 
be twice as great as the moment of the force transmitted from either C 
or Ci to D. That is, the sum of the moments applied to C and Ci must 
equal the moment applied to B. If, therefore, 1 is the length (feet) of 
the arm at which the weight w (pounds) is applied, and n is the number 
of revolutions per minute of the shaft A, then the power transmitted 

PER MINUTE = 

(foot-pounds), (30) 



and 



Horse power (h.p.) = 



xlnw 
33,000 



(3i) 



MEASUREMENT OF POWER — DYNAMOMETERS 167 

Now if the lever L is to be prevented from turning about its axis, a 
couple will be required which is twice the driving couple being trans- 
mitted. If, then, a weight of w pounds sliding on L as shown in the 
figure is placed at a distance 1 feet from the axis, so that the lever remains 
horizontal, the driving couple can be determined; and when the revolu- 
tions of the shaft A are known, the power can be found. A dash-pot D 
is usually attached to the differential lever L to reduce vibrations. This 
dash-pot should always be kept filled with glycerine or good clean oil. 
If the dash-pot is sticky consistent results cannot be expected. 

A Webber Differential Transmission Dynamometer as made commer- 
cially is illustrated in Fig. 203. The scale on the lever arm of this instru- 




Fig. 203. — Webber Differential Transmission Dynamometer. 



ment is graduated into 100 divisions and a bell is provided which rings 
at every 100 revolutions. Since the horse power transmitted in one 
-n-lnw 



revolution per minute is 



equation (31), then the horse power 



33,000' 

corresponding to one division on the scale per 100 revolutions per minute 

is also for a perfect calibration. 

33,000 



168 POWER PLANT TESTING 

It is interesting to observe that if we let 
v = the vertical force acting at C and Ci; 

p = the vertical pressure between the teeth at each point of contact; 
d = distance from the center of the rotation to C and Ci; 
1 = the distance from the same center to the weight w. 

Then from the foregoing discussion it should be clear that 2 v = 4 p 
and wl = 2 vd = 4 pd. If r is the effective pitch radius of the driving 
gear wheel B, ri is the radius of the small bevel wheels, and the force pro- 
ducing the turning movement in the shaft A is represented by f , we have, 

fr = 2 pri, 
and 

, 2pri wlri ' 

f = -r = idr (32) 

If we know the number of revolutions, then the space passed through 
by the force f can be calculated, and the work in foot-pounds is the prod- 
uct of the force times the distance passed through. The units given 
above are of course respectively in feet and pounds. 

About ten horse power can be transmitted and measured by one of 
these instruments having wheels B and D about ten inches in diameter, 
when operating at 800 revolutions per minute. 1 Wear on the gears and 
noise becomes excessive at higher power and speed. 

Calibration of a Differential Dynamometer. 1. Examine the dash- 
pot and observe whether the piston moves freely in the cylinder, par- 
ticularly without " sticking." After the apparatus has been well oiled 
the position of the poise to make the lever arm horizontal should be 
observed for " no load." If this is not at zero then all the readings on 
the scale must be corrected by the amount of this zero reading. 

2. At each of the speeds required make a preliminary run without 
load and observe the reading of the poise when the lever is balanced. 

3. Attach a Prony brake to the shaft from which the power is to be 
transmitted and observe for a series of loads and speeds the readings of 
the poise on the dynamometer lever. 

4. For each speed plot a curve with theoretical foot-pounds per 
minute by equation (30) as abscissas and actual foot-pounds per minute 
as determined by the Prony brake as ordinates. 

Emerson Power Scales. . Another very satisfactory instrument for 
the measuring of power transmitted by shafting is known as the Emer- 
son Power Scales. It is illustrated in Fig. 204. 

It consists of a pulley C keyed to the shaft. To this pulley C a wheel 
B is connected loosely by studs EE projecting between and bearing 
against its spokes. The pressure exerted on these studs is proportional 

1 S. S. and W. O. Webber, Trans. Am. Soc. M. E., vol. 4, page 227. 



MEASUREMENT OF POWER — DYNAMOMETERS 169 



to the power transmitted by means of the pulley C, and this pressure is 
transmitted by a system of levers LL and bell-cranks MM to a sleeve 
A connected to a " weighing 
lever " W. The sleeve slides 
loosely on the main shaft. The 
amount of the pressure exerted 
on the studs is indicated for 
small values by a pointer P, 
moving over a graduated scale 
F. For pressures beyond the 
limits of the graduated scale 
weights are placed on the scale 
pan N. A dash-pot D is pro- 
vided to prevent excessive vi- 
brations and make the pointer 
" dead-beat." 

The scale F is calibrated to 
read the pressure (force) exerted 
by the torque of the pulleys C 
on the studs E in pounds. The 
work or "power" is calculated, 
therefore, by taking the product 
of this force times the distance 
moved through. If d is the 
diametral distance between the 
centers of the studs in feet, n the revolutions per minute and w the read- 
ing of the scales, then, 

, xdnw 

Horse power 1 = . 

33,000 




— Emerson Power Scales. 



(33) 



A speed counter is attached to the apparatus for counting the num- 
ber of revolutions. This apparatus is made by the Florence- Machine 
Co., Florence, Mass. 

Flather's Hydraulic Transmission Dynamometers. A form of trans- 
mission dynamometer which is operated by hydraulic pressure is shown 
in Fig. 205. The power shaft is keyed to the boss of a pulley B with 
two or more arms carrying hydraulic cylinders R. Projecting ends or 
studs from these cylinders bear upon the arms of a loose pulley A on 
the same shaft. The torque imparted by the driving belt to the loose 
pulley A is thus transmitted to the shaft S through the liquid, and the 
resulting pressure is conveyed by radial pipes U to the hollow central 
shaft, and then to a pressure gage G. The hollow shaft is always filled 



Compare with (31) for differential dynamometers, page 166. 



170 



POWER PLANT TESTING 



with oil. In the figure an engine indicator I is shown attached to the 
hollow shaft for recording the pressure. The loose pulley A drives the 
tight pulley B through its pistons which press on the oil in the cylinders 
carried by the tight pulley. By means of a worm drive the drum of 
the indicator receives its motion from the central shaft S. Figs. 206 
and 207 show more in detail the construction of the hydraulic cylinders 
on the pulley B. Fig. 208 shows typical indicator diagrams from this 




Fig. 205. — Flather's Hydraulic Transmission Dynamometer. 



apparatus. Both were taken from a dynamometer connected to a 
mining drill. The first was taken when the drill was sharp, the second 
when it was dull. 

Among the advantages claimed are: (1) its simplicity, (2) that it is 
not appreciably affected by the velocity of the shafting, (3) that no 
countershaft is required, (4) by connecting it to a recording gage a con- 
tinuous diagram of the load can be obtained. 

Torsion or Shaft Dynamometers. When a shaft is subjected to a 
twisting moment an angular twist is produced which is proportional to 



MEASUREMENT OF POWER — DYNAMOMETERS 171 




Fig. 206. — Diagram Showing Pulleys, Pistons, and Shaft of Flather's Dynamometer. 




Fig. 207. — Details of Pistons and Cylinders in Flather's Dynamometer. 



-At^iff^ 



^\/Y /VA/ V/ r/ K 



Fig. 208. — Indicator Diagrams from Flather's Dynamometer Attached to a Mining 

Drill. 



172 POWER PLANT TESTING 

that moment. Thus if 6 is the angle of twist produced by a twisting 
moment T in inch-pounds and if n is r.p.m., then 

2 xTn 

b.h.p. = — . 

12 X 33jQoo 

Torsion meters, shown in Figs. 209, 210, 211 and 212, although ap- 
plicable to large as well as small powers, have their most important ap- 
plications for measuring shaft horse power of marine turbines and engines. 

A Shaft Dynamometer consists essentially of a long metal tube en- 
circling the shaft and fastened to it at one end, but free at the other 
and is maintained in alignment by adjustable rollers; two radial arms, 
one attached to the shaft and the other to the free end of the tube, 
which rotate a slight amount with reference to each other, according 
to the twist of the enclosed length of shaft; and a set of levers which 
multiply this rotative movement and at the same time convert it into 
linear motion, which is transmitted to a sleeve and collar mounted, 
upon the shaft and sliding thereon. These parts all revolve with the 
shaft. An independent indicating apparatus is provided, which is 
mounted on a stationary frame, and the sliding movements of the rotat- 
ing collar is transmitted through it to an index hand. The torsional 
strain is determined from the reading of the accompanying scale, which 
is graduated to millimeters. 

The zero reading is found by disconnecting the propeller and turning 
the shaft at a slow speed, first in one direction and then in the other, 
observing the indication in both cases, and fixing the point of zero strain 
at the mean of the two. When it is impracticable to disconnect the 
propeller the readings may be taken when the vessel is drifting under her 
own headway after shutting off steam. The calibration of the instru- 
ment, which can best be done when the shaft is in the shop before 
installation, is carried on by securing the shaft in a fixed position, and ap- 
plying a torsional strain by means of weights at the end of a lever at- 
tached beyond the dynamometer, taking readings with a number of 
different weights. 

The horse power shown by the dynamometer is determined by mul- 
tiplying the reading of the instrument expressed in millimeters by the 
number of revolutions of the shaft per minute, and by a constant de- 
termined from the calibration. The constant is an expression for the 
horse power corresponding to a speed of one revolution per minute and 
a reading of one millimeter. 

A shaft dynamometer requires very delicate adjustment as such instru- 
ments used on large steam turbines and engines requiring a shaft of com- 
paratively large size, require a movement at the end of the two arms of 
only one hundredth of an inch to produce a change of 500 horse 
power in the load being transmitted. 



MEASUREMENT OF POWER — DYNAMOMETERS 173 




Fig. 209. — Spring Dynamometer. 




Fig. 210. — Mechanically Operated Shaft Dynamometer. 




Electro-Magnet 



Telephone 
Handwheel N p^- / Receiver 
with Scale 



Fig. 211. — Electrically Operated Shaft Dynamometer. 




Fig. 212. — Shaft Dynamometer with Optical Means of Observation. 



174 



POWER PLANT TESTING 



Kenerson Torsion Dynamometer 1 (Figs. 213 and 214) consists essen- 
tially of a divided shaft with a flanged coupling rigidly fastened to each 

of the adjoining ends. These 
io Gage, fl fl T T E Jj. flanges are only loosely con- 

nected by stud bolts and 
"latches." The latter are 
twisted by the power impressed 
so that their ends are forced 
against a pressure plate. The 
pressure against this plate is a 
measure of the power trans- 
mitted. Ball-bearing races 
attached to a diaphragm covering 
an oil chamber communicate this 
pressure or thrust to a chamber 
in which the pressure is indicated 
by a Bourdon gage. Readings must be corrected for static head if the 
gage is placed above or below the couplings. 

The accelerometer shown in Fig. 215 is used a great deal in automobile 
testing. From the indications of this instrument in terms of acceleration 




213. — Kenerson Dynamometer. 




Fig. 214. — Parts of Kenerson Dynamometer. 

the power developed can be computed. 2 This instrument is designed on 
the principle that a pendulum hung on a moving body will be in a vertical 
position when at rest and moving uniformly. In 
the figure D is a copper disk pivoted on a rotating 
vertical axis, M is a magnet for dampening the move- 
ment of this disk, and G shows two gear wheels of 
equal diameter, one fastened to the axis supporting 
the disk and the other on a separate axis carrying 
the needle N. A coil spring brings the needle back 
to zero. One side of the disk D is heavier than the FlG - 215.— Acceler- 
other, so that when the acceleration takes place in 

1 Transactions American Society of Mechanical Engineers, vol. 31 (1909), pages 171 
to 179. 

2 Internal Combustion Engineering, (London), Oct. 2, 1912, and Engineering, Sept. 16, 
1910. 




.Direction cf Motion 



MEASUREMENT OF POWER — DYNAMOMETERS 175 

the direction of the arrow the heavier side tends to lag behind, causing a 
movement of the gears and the needle. 

If F is the total resistance in pounds per ton at N miles per hour and 
W is the weight of the vehicle in tons, then brake horse power equals 
F X W X N divided by a constant. 



CHAPTER VII 

FLOW OF FLUIDS 

The flow of fluids will be discussed under these heads : 

1. The flow of air. 

2. The flow of steam. 

3. The flow of water. 

The Flow of Air. When subjected to only a.low pressure, air and many 
other gases are usually measured by a gas meter, of which there are many 
types sold commercially. There are, however, two general types: (1) 
"wet" and (2) "dry.". The former is by far the more reliable and 
should be always used in preference to a " dry " meter when it can be 
obtained. " Wet " meters receive their name from the water seal main- 
tained in them. This seal must be always kept at a constant level, de- 
termined by calibration, and before using such a meter in a test one 
should always observe whether the water level is at the standard mark. 
If it is not, then water must be added or withdrawn as the case may be. 
A section of a" wet " meter is shown in Fig. 220. It consists of a rotor 
somewhat resembling a paddle wheel revolving on a horizontal axis in 
an enclosed cylindrical casing partly filled with water. Fig. 221 illus- 
trates a typical apparatus of this kind, with four compartments A, B, C 
and D. When air or any gas flows 1 into one of the chambers of the meter 
it accumulates over the surface of the water and by its pressure raises 
the chamber until it is filled. 

During rotation, by means of the water seal the central ports a, b, c 
and d are opened and closed. When these are open gas from the pipe at 
the gas inlet is admitted to the compartments out of the water. Discharge 
ports a', b', c' and d' through which the gas passes to the discharge pipe are 
also opened and closed by the water seal. If the drum revolves freely no 
gas can pass through the meter without producing the required move- 
ment of the recording mechanism, because the admission and discharge 
ports will not be open simultaneously in any compartment. Even the 
smallest rates of flow are accurately measured. Rotation is due to the 
difference in water level, as shown in the figure, between the two sides 
when the meter is operating. In the figure gas is being admitted on the 
left-hand side so that the pressure on that side will be slightly greater 

1 The nature or specific gravity of the gas is not important, as gas meters are cali- 
brated to record volumes, usually cubic feet. 

176 



FLOW OF FLUIDS 



177 



than on the right, causing the water level to be higher and making a 
greater weight on the right-hand side than on the left. On account of the 




Fig. 220. — Typical "Wet" Gas Meter. 

difficulty in making the admission and discharge ports of the rotor of suffi- 
cient size the admission ports are usually placed at one end and the dis- 




Gas Enters 



Fig. 221. — Diagram of "Wet " Gas 
Meter. 




Fig. 222. — Rotor of " Wet " Gas 
Meter. 



charge ports at the other, as illustrated in Fig. 222, the flow of gas being 
shown by the arrows. In the assembled view (Fig. 220) the gas enters at 
the dry-well, V, passes through the drum and out at the front end, then 



178 POWER PLANT TESTING 

over the drum between it and the case to the outlet. 1 In this way the 
drum is made to revolve to the left by the pressure on the surface of the 
water below and the slanted partition C above, forming an ever-increas- 
ing pyramidal space between the surface of the water and the plane 
of the slanted partition. 

Fluctuations of pressure or of velocity cause errors only when great 
enough to produce a sufficient surging of the water, so that the water 
sealing on the valves may at times be prevented. If the flow is inter- 
mittent as in the suction pipe of gas engines and compressors a pressure 
regulator must be provided. A rubber bag is used as a regulator when 
the gas is under pressure and a diving bell hung on springs for suction 
gas. 

" Dry " Gas Meters are used for the usual " house metering " of gas. 
They are not nearly so accurate as the " wet " types, but can be used 
more conveniently because they are not dependent on a constantly 
maintained water level. In simplest terms such meters consist of two 
chambers separated by a vertical partition, each chamber containing an 
interior measuring receiver having a flexible shell. Gas is admitted to 
these measuring receivers alternately by means of slide valves actuated 
automatically. The reciprocating movement of alternately filling and 
emptying these receivers operates the counting mechanism. 

" Wet " meters are usually very accurate, while " dry " meters are 
not " supposed to be instruments of great accuracy." 

Pitot Tube for Measurement of Air. Probably the most accurate 
method of measuring air in large volumes is by means of a Pitot tube. A 
standard instrument of this kind designed for the measurement of air by 
the American Blower Company is shown in Fig. 223. 

It consists simply of two concentric brass tubes, a small one A being 
placed inside of a larger one B, as illustrated in detail in Fig. 224. These 
tubes are arranged so that each has a separate connection, as at A' and 
B'. The lower end of the small tube is open at A, while the outside and 
larger tube is tapered and closed; but approximately midway along 
its horizontal portion, as shown in the figure, there are two holes on 
each side. 2 These holes should be not much more than /„ inch in di- 
ameter. 

The Taylor Pitot tube was formerly much used. It differs essentially 
from the one shown in the figures by having a short slot 2| inches long 
and T V inch wide on each side. At high velocities these slots cause 

1 More frequently the outlet for the gas is on the top of the casing than at the back 
as shown in the figure. 

2 The holes for static pressure are shown here at the top and bottom. In practice 
these holes are usually placed at the sides of the tube as in this location they are less 
likely to become filled with dust and refuse. 



FLOW OF FLUIDS 



179 



eddies 1 and the static pressure observed will be too high. Taylor tubes 
being 13 inches long compared with 4| inches for the ABC types are 
much more clumsy and liable to breakage in handling. 

When the instrument is used it is placed so that the opening at A points 
against the direction of flow and receives the full effect of the pressure 
due to the velocity of flow. The side openings in B are subjected to only 




Fig 



223. — " American Blower Co 
Standard Pitot Tube. 



Fig. 224. — Section of Pitot Tube. 




the static pressure. For convenience let p = velocity pressure and s = 
static pressure. For example, the difference in the levels in the manom- 
eter, a, Fig. 226, is therefore that due to (p + s) — s, or simply p, the 
velocity pressure. 

Another type of Pitot tube much used and known as Burnham's is 
shown in Fig. 225. It is made up of two tubes A and B. Tube A is for 
obtaining the total pressure and in principle is not 
different from those already described. The static 
tube B is unique. It is open at the end and is 
pointed downward. On the side toward the direc- 
tion of flow it is beveled at an angle of about 45 
degrees. Neither the Taylor nor the Burnham 
types are satisfactory for measuring velocities above 
6,000 to 8,000 feet per minute, while the ABC type 
is accurate for very high velocities. The latter 
type is the one recommended by the Power Test Committee of the 
A.S.M.E. (see Journal, Nov., 1912, page 1831). 

Pitot tubes are usually connected to manometers or preferably to 
sensitive draft gages, showing the pressure in small fractions of an inch 
of water. When the end of the Pitot tube at A' is connected to the 
left-hand end of a draft gage, like those in the figures on page 182, and the 
end at B' is attached to the right-hand end, the instrument acts as a 
differential gage and the difference between the reading when thus con- 
nected and its zero reading is the pressure in inches of water corre- 

1 This inaccuracy of the Taylor type of tube can be remedied by soldering neatly 
a sheet of fine brass gauze over the slots. For results of tests with the Taylor tube 
see Trans. A.S.M.E., vol. 33 (1911), pages 1137-1173. 



Fig. 225. — Burnham's 
Pitot Tube. 



180 POWER PLANT TESTING 

sponding to the velocity alone; that is (p + s) — s. If, as before, we 
call the velocity pressure F in inches of water, and if h is the height or 
" head " in feet of an equivalent column of air producing the same 
pressure, then the velocity of the air v in feet per minute is 

v = 60 V2 gh, 

where g is the force of gravity (32.2), and 

wt. of a cu.;f t. of water 1 



h = -^X 



12 wt. of a cu. ft. of air 

62.3 p 5.196 p 



12 X wt. cu. ft. air wt. cu. ft. air' 



Y = I W w t.cu P ft.air (34) 

In the following table the weight is given of dry air and also the 
weight of air completely saturated with moisture (100 per cent humidity). 
The data given are at atmospheric pressure (14.7 pounds per square 
inch) and the temperature given is that indicated by the " dry " 
thermometer. By interpolating between these tables, the weight of 
air for any temperature and degree of saturation is easily obtained. 
Remembering also that the weight per cubic foot is directly proportional 
to the absolute pressure, the weight for any pressure is readily de- 
termined. Tables for determining the percentage of saturation by means 
of wet- and dry-bulb thermometers are given on page 368. 

For many engineering calculations relating to tests of fans and blowers 
it is accurate enough to interpolate between columns (3) and (4) to allow 
for humidity. For work requiring greater accuracy use the curve sheets 
given on pages 1006 and 1007 in the Transactions of A.S.M.E., vol. 33. 
Observe that the numbers on the curved lines on page 1006 should be 
marked per cent instead of degrees. 

To determine the volume of air flowing through a circular duct, the 
average velocity is most accurately obtained by dividing the cross- 
section of the duct or pipe into 5 or 10 imaginary annular rings of equal 
area. Each of these rings is then again divided into two others of 
equal area. Observations for a given flow are then made by shifting 
the Pitot tube rapidly along a diameter and taking readings with the 
tip of the tube at each of these last points of subdivision, called 
" stations." Average velocities and flows are then readily obtained from 
these observations. This is sometimes known as the " ten point " method. 
For a pipe of radius r, divided into five annular rings, the " stations " 

1 The weight of a cubic foot of water at about "room" temperature (about 70 deg. 
Fahr.) is about 62.3 pounds. 



FLOW OF FLUIDS 



181 



PROPERTIES OF AIR.* 





Weight of 


Specific Volume, Cu. Ft. 




Weight of 
Water 

Vapor per 
Pound 


Specific Volume, Cu. Ft. 


Temp, by 
Dry Bulb, 


Water 

Vapor per 

Pound 


per Lb. 


Temp, by 

Dry Bulb, 

Deg. F. 


per Lb. 


Deg. F. 












Pure Air, 
Lbs. 


Dry Air. 


100% Satu- 




Pure Air, 


Dry Air. 


100% Satu- 






rated Air. 




Lbs. 




rated Air. 


(1) 


(2) 


(3) 


(4) 


(1) 


(2) 


(3) 


(4) 





.0009 


11.588 


11.603 


74 


.0179 


13.449 


13.593 


10 


.0016 


11.795 


11.820 


76 


.0192 


13.499 


13.654 


20 


.0024 


12.051 


12.091 


78 


.0206 


13.549 


13.715 


32 


.0038 


12.388 


12.414 


80 


.0220 


13.600 


13.777 


34 


.0041 


12.439 


12.469 


82 


.0235 


13.650 


13.841 


36 


.0044 


12.489 


12.523 


84 


.0252 


13.701 


13.906 


38 


.0047 


12.539 


12.576 


86 


.0269 


13.752 


13.971 


40 


.0051 


12.590 


12.629 


88 


.0288 


13.801 


14.038 


42 


.0055 


12.640 


12.682 


90 


.0307 


13.852 


14.106 


44 


.0060 


12.692. 


12.736 


92 


.0328 


13.903 


14.173 


46 


.0065 


12.741 


12.791 


94 


.0350 


13.954 


14.241 


48 


.0070 


12.792 


12.846 


96 


.0374 


14.004 


14.310 


50 


.0076 


12.842 


12.901 


98 


.0399 


14.055 


14.382 


52 


.0082 


12.893 


12.957 


100 


.0424 


14.106 


14.455 


54 


.0088 


12.944 


13.012 


105 


.0500 


14.232 


14.643 


56 


.0094 


12.993 


13.068 


110 


.0586 


14.358 


14.840 


58 


.0100 


13.044 


13.124 


115 


.0687 


14.484 


15.050 


60 


.0108 


13.095 


13.180 


120 


.0804 


14.611 


15.272 


62 


.0117 


13.146 


13.240 


125 


.0941 


14.736 


15.509 


64 


.0126 


13.196 


13.298 


130 


.1102 


14.863 


15.761 


66 


.0135 


13.246 


13.354 


135 


.1293 


14.959 


16.032 


68 


.0145 


13.298 


13.413 


140 


.1515 


15.116 


16.325 


70 


.0156 


13.348 


13.471 


145 


.1782 


15.242 


16.643 


72 


.0167 


13.398 


13.532 


150 


.2100 


15.368 


16.993 



1 W. H. Carrier in the Transactions of A.S.M.E., vol. 33 (1911) pages 1005-1136. 
These table are generally considered more reliable than any other available data. The 
tables of the U. S. Weather Bureau are in error because they were computed on the 
assumption that saturated air is a perfect gas. The fallacy is particularly observable 
at high temperatures. 



or points of observation would be at the following distances from the 
center: (1) 0.316 r; (2) 0.548 r; (3) 0.707 r; (4) 0.837 r; (5) 0.949 r. 

When the Burnham Pitot tube is used readings are taken usually in 
only one position. This position giving the average velocity is stated to 
be at a distance of T 8 o of the actual internal radius from the center of 
the pipe. 

Ducts of square or rectangular section are usually divided up simi- 
larly into a series of elementary squares or rectangles. 

Figs. 226 and 227 show the methods of connecting a Pitot tube to 
manometers for observing velocities when the pressure is above or 
below atmospheric. The usual case is where the pressure is greater than 
atmospheric, and the cases where it is less are most often in the suction line 
of a ventilating fan. In Fig. 227 positions of "stations " (a, b, c, and d) are 



182 



POWER PLANT TESTING 



marked on a board to assist in taking observations. Measurements of 
velocity with a Pitot tube should not be attempted if there is not at 
least 15 feet of straight pipe in the direction in which the tube is pointed. 
This precaution is necessary to avoid the effect of eddies in the pipe. 




For Pressures above Atmospheric 



For Pressures less than 
Atmospheric 

Fig. 226. Fig. 227. 

Arrangement of Connections for Pitot Tube Measurements. 



Anemometers. A very convenient and simple method for measuring 
directly the volume of the air, or any gases, is by using an instrument 
called an anemometer. This instrument, Fig. 228, consists in its essen- 
tial parts of a light vane wheel like 
a screw-propeller having either flat 
or lightly curved vanes mounted on 
slender arms. The wheel must be 
made very light in weight, must be 
accurately balanced, and should move 
easily in its bearings. By its own 
motion it operates a counting me- 
chanism attached to its shaft which 
indicates velocities in feet. Readings 
of the counter are taken at the be- 
ginning and end of a suitable lapse 
of time, usually \ to 1 minute. Such 
instruments must be placed with the 
axis of rotation in the direction of 
the flow of air or gas. They have 
upper and lower velocity limits be- 
yond which they should not be used. 
The lower limit cannot be defined 
as it will depend on the precautions 
taken in manufacture and in use to 
eliminate friction. As regards the 
higher limit, it will usually depend on the size of the wheel, large wheels 
being less suitable than smaller ones for high velocities. Practically 
none should be used for velocities higher than 1,000 feet per minute. 




228. — A Typical Anemometer for 
Measuring Velocity of Air. 



FLOW OF FLUIDS 



183 




A calibration chart must always be provided for such instruments 
and the calibration should be frequently checked at several points 
within its velocity limits. 

Methods of Calibrating Anemometers, Pitot Tubes, and Gas Meters. 
Probably the best method of calibrating anemometers is to compare their 
readings with the actual measurements of air 
discharged from a gasometer or gas-holder like 
Fig. 229. It consists of a tank A for holding 
water or other liquid into which the "bell" B 
is raised and lowered. The piping as shown is 
arranged with a three-way cock (see page 139), 
but for accurate work separate inlet and dis- 
charge pipes should be provided. The weight 
W is to counterbalance the weight of the bell. 
This method of counterbalancing if used without 
a means for correction would cause a change of 
pressure of the gas in the holder as the bell 
ascends or descends, due to a variation of depth 
of immersion. As a means to correct this, a 
compensating weight w is suspended from a cord 
wrapping over a can C. Observations required 
to determine volume of gas are (1) pressure (usu- 
ally read with a water manometer M) (2) tem- 
perature; and (3) movement of the bell in a given time. In order to 
get the temperature of the gas in the bell accurately the temperature 
of the liquid should be as nearly as possible the same as that of the 
gas. Movement of the bell is usually read directly with the help of a 
suitable scale and some form of sighting device to insure accuracy in 
reading the scale. 

Gasometers may be calibrated by calculation or by actual tests, pref- 
erably on the displacement of water. When the method of calculation 
is used, measurements of the diameter should be made at several points 
on the circumference to allow for possible lack of symmetry. 

Large gasometers such as are installed at gas works are also fre- 
quently used to calibrate Pitot tubes; and gas meters are invariably 
calibrated by comparison with a gasometer. 

Gas meters may also be calibrated by any apparatus suitable for the 
displacement of the gas as it is withdrawn by water or other suitable 
liquid. It is very necessary, of course, that when the weighings are 
made the pressure and temperature of the gas be accurately deter- 
mined. 

Anemometers are suitable only for low velocities (from about 50 to 
1500 feet per minute) and Pitot tubes in general are best adapted to 



Fig. 229. — Gasometer. 



184 POWER PLANT TESTING 

velocities from 300 to 3000 feet per minute, but instruments like the 
"A. B. C." type (Fig. 223) designed to avoid eddies around the "static " 
openings are satisfactory up to 6000 feet per minute. 

In order to use an anemometer successfully all the gas to be measured 
must be passed through openings of suitable size in which the instru- 
ment can be placed. These openings should each have an area of 
about 15 square inches (if the anemometer is about 2| inches in diam- 
eter) so that the resistance interposed by the instrument will be 
negligible. 

A very common method of calibrating anemometers and Pitot tubes 
is by mounting them on the end of a long and light rod arranged to be 
revolved about a central point. The readings of the instrument are 
compared with its computed velocity. Other methods of calibration 
under more nearly " working conditions " are generally considered better, 
as the method of swinging about a central point makes the instrument 
read too high on account of the eddies produced. 

" The standard of reference for calibrating Pitot tubes, anemometers, 
etc., is the gasometer, 1 and if the instrument used cannot be calibrated 
by actual measurement, the constants employed should be those ob- 
tained from a similar instrument which has been calibrated by actual 
reference to a gasometer measurement." (Report of Power Test Com- 
mittee, A.S.M.E, Nov., 1912.) 

Flow of Air through an Orifice. Air under comparatively high pres- 
sures is usually measured in practice by means of pressure and tempera- 





Fig. 230. — Measuring Flow of Air through an Orifice. 

ture observations made on the two sides of a sharp-edged orifice in a 
diaphragm. Fig. 230 illustrates the method with two pressure gages on 
opposite sides of the orifice and a thermometer for obtaining the tem- 

1 It is very difficult to get a uniform temperature in a gasometer so that the vol- 
ume of gas discharging from the outlet may be different by 2 or 3 per cent from that in- 
dicated by the scale on the gasometer. When accurate work is to be done a better 
method to use is the displacement of water as measured by its weight in a vessel of 
heavy sheet metal. The walls of the vessel should be heavy to prevent rapid radiation 
to the surrounding air. A long thermometer should be used which should be inside 
the vessel itself and may be read through a peep-hole. If the vessel is of heavy glass 
the conditions will be still better. 



FLOW OF FLUIDS 185 

perature ti at the initial or higher pressure p x . The flow of air w, in 
pounds per second, may then be calculated by Fliegner's formulas. 

w = .530 X a * ■ when p x is greater than 2 p 2 (45) 

vTi 

w = 1.060 X a y T when pi is less than 2 p 2 , . . (46) 

where a is the area of the orifice in square inches, Ti is the absolute initial 
temperature in degrees Fahrenheit at the absolute pressure p L in the 
" reservoir or high-pressure side " and p 2 is the absolute discharge pres- 
sure, both in pounds per square inch. When the discharge from the 
orifice is directly into the atmosphere, p 2 is obviously barometric pressure. 

For small pressures it is often desirable to substitute manometers for 
pressure gages. One leg of a U-tube manometer can be connected to 
the high-pressure side of the orifice and the other leg to the low-pressure 
side. Many engineers insert valves or cocks between the manometer 
and the pipe in which the pressure is to be observed for the purpose of 
" dampening " oscillations. This practice is not to be recommended as 
there is always the possibility that the pressure is being throttled. 1 A 
better method is to use a U-tube made with a restricted area at the bend 
between the two legs. This will reduce oscillations and not affect the 
accuracy of the observations. 

Discharge from compressors and the air supply for gas engines are 
frequently measured by orifice methods. 

When pi — p 2 is small compared with pi, the simple law of discharge 2 
of fluids can be used as follows: 

w = -£- V2 g X 144 (Pi - P2) s, (47) 

144 

1 Report of Power Test Committee, Journal A.S.M.E., Nov., 1912, page 1695. 

2 If the density is fairly constant, 

144 Pi , Vl 2 _ 144 P2 Vo 2 

■ i ' — t" > 

S 2 g S 2g 

where Vi is the velocity in feet per second in the "approach" to the orifice and v is the 
velocity in the orifice itself. Since Vi should be very small compared with Vo, 
V 144 (pi - P2) 

2g S 



Vo=\/ : 



2 g X 144 (Pi - Pa) 



fa Vo s , . / 2 g X 144 (P i - P2) 

w = = fas V , 

144 V s 



•w= — V2 g X 144 (pi - P2) s. 
144 



186 POWER PLANT TESTING 

where w is the weight in pounds discharged per second, a is the area of 
smallest section of orifice in square inches, the pressures pi and p 2 are in 
pounds per square inch, f is a coefficient from experiments, g is the accel- 
eration due to gravity (32.2), and s is the unit weight of the gas meas- 
ured, in pounds per cubic foot, for the average of the initial and final 
conditions of temperature and pressure (Table of weight of air on page 
181). If the difference in pressure is measured in inches of water h with 
a manometer then 

144 (pi — p 2 ) = - — — X h, (lbs. per sq. ft.) 



^y 2ghs X-~, (lbs. per sec), 



where 62.4 is the weight of a cubic feet of water (density) at usual "room" 
temperatures. 

This equation can also be transformed so that a table of the weight of 
air is not needed, since by elementary thermodynamics 144 pv = 53.3 T, 
where v is the volume in cubic feet of one pound of air or other gas and 
T is the absolute temperature in degrees Fahrenheit. Since v is the 
reciprocal of s, then 

s = 144 p -f- 53.3 f , and 

i7~~ I 

w = .2opfay/^ (48) 

Here p and T should be the values obtained by averaging the initial and 
final pressures and temperatures. Great care should be exercised in 
obtaining correct temperatures. When equation (47) is used, for accu- 
rate work, corrections of s for humidity must be made. 1 

For measurements made with orifices with a well-rounded entrance 
and a smooth bore so that there is practically no contraction of the jet 
the coefficient f in equations (47) and (48) may be taken as 0.98. In 
the rounding portion of the entrance to such a nozzle the largest diameter 
must be at least twice the diameter of the smallest section. For circular 
orifices with sharp corners Professor Dalby 2 in reporting very recent 
experiments stated that the coefficient for his sharp-edged orifices in a 
thin plate of various sizes from 1 inch to 5 inches in diameter was in all 
cases approximately .60; and these data agree very well with those 
published by Durley. 3 

1 Tables of humidity are given on page 368. 

2 Engineering (London), Sept. 9, 1910, page 380, and Ashcroft in Proc. Institution of 
Civil Engineers, vol. 173, page 289. 

3 Transactions American Society of Mechanical Engineers, vol. 27 (1905), page 193. 



FLOW OF FLUIDS 



187 



When p 2 -j- pi = .99 the values obtained with this coefficient are in 
error less than § per cent; and when p2-^Pi = .93 the error is less than 
2 per cent. 

Flow of Air Measured by Cooling. This method depends on taking 
from the air an amount of heat 1 which can be measured and then 
computing from the heat units absorbed, the difference in temperature, 
and specific heat of the air, its weight and volume. 2 The arrangement 
of the apparatus is shown in Fig. 231. A coil of pipes C, of which the 
cooling surface is as equally as possible distributed over the section of 
the duct D, D', carrying the air to be measured, is used to absorb heat 
by circulating water through it. Thermometers are arranged so that 
the temperatures of the air and of the water can be observed, and a 



S 11 I 



4J 



1 



f 



Fig. 231. — Measuring Flow of Air by Cooling. 

platform scales is shown for obtaining the weight of water. Using the 
symbols ti and t 2 for the initial and final temperatures of the air in de- 
grees Fahrenheit, t' and t" for the temperatures of the water entering 
and leaving in degrees Fahrenheit, w a = weight of air passing through 
duct in pounds per second, w === weight of water collected in pounds 
per second, and .2375 = specific heat of the air at constant pressure 
and at temperatures not much above " atmospheric," then the heat 
absorbed by the water per second is w (t" — t' ), B.t.u. and this equals 
the heat lost by the air, or .2375 w a (ti — t 2 ), and therefore 

w (t"-t') 4.2 1 1 Wo <t" -t') 



.2375 (ti - t 2 ) 



(ti - t 2 ) 



(49) 



1 The method will be equally applicable if heat is added, as for example by passing 
steam through the coil. This method is often used to calibrate Pitot tubes and ane- 
mometers. 

2 The weight of a cubic foot of air is .0765 pound at 62 (522 abs.) degrees Fahrenheit 
and 14.7 pounds per square inch pressure. Since the volume is directly proportional 
to the absolute temperature, the weight at any other temperature is easily computed. 



188 POWER PLANT TESTING 

Thomas' electric meters employ this method of measuring gas, using 
electric current for the heating medium. The gas flows past a series of 
electrical resistances enclosed in a pipe. Electric heating by these 
resistances raises the temperature of the gas a few degrees. Tempera- 
tures before and after heating are measured by delicate resistance 
thermometers connected to a Wheatstone bridge and a sensitive 
galvanometer. 

If the electrical energy used for heating be kept constant, and if the 
specific heat of the gas does not vary, the flow is inversely proportional 
to the rise in temperature. 

If E is the amount of energy in watts, supplied to raise the temper- 
ature of w pounds of gas per hour through t degrees Fahrenheit and C is 
the specific heat of the gas at constant pressure, then 

34 I2E '(„ \ 

W= ^- (50) 

If the volume of gas is required, its pressure, temperature and relative 
humidity must be determined. 

Receiver Method of Measuring Air. None of the preceding methods 
are adaptable for measuring the volume of air at high pressures as in 
the case of measuring the discharge in tests of air compressors. Pump- 
ing air into a suitably strong receiver is a method often used. The 
compressor is made to pump against any desired pressure which is 
kept constant by a regulating valve on the discharge pipe: 

Pi and P 2 = absolute initial and final pressures for the test, pounds 
per square inch. 

Ti and T 2 = mean absolute initial and final temperatures, degrees 
Fahrenheit. 

Wi and W 2 = initial and final weight of air in the receiver, pounds. 

V = volume of receiver, cubic feet. 

PiV = WRTi, and P 2 V = W 2 RT 2 , where R is the constant 53.3 for 
air, then weight of air pumped, 

w >- w > = i-M-%) (5I) 

In accurate laboratory tests the humidity of the air entering the com- 
pressor should be measured in order to reduce this weight of air to the 
corresponding equivalent volume at atmospheric pressure and temper- 
ature. 

Principal errors in this method are due to difficulty in measuring the 
average temperature in the receiver. Whenever practicable the final 
pressure should be maintained in the receiver at the end of the test until 
the final temperature is fairly constant. 



FLOW OF FLUIDS 189 

The above method is often reversed by discharging air at high pres- 
sure from a receiver. Constant discharge pressure is maintained by 
throttling with a valve. 

Measurement of Air by Chemical Analysis. Quantity of air supplied 
for combustion in boilers and other furnaces can be determined from 
the analysis of the products of combustion by the formulas given on 
pages 251 and 281. 

Venturi Meters (see page 199) are also used successfully for measur- 
ing large volumes of gas as in tests of gas producers/ etc. 

The Flow of Steam through Nozzles and Orifices. The flow of the 
steam from an orifice or nozzle has a very definite critical value when 
the final pressure is approximately 0.58 of the initial pressure. When 
the final pressure is less than this critical value the flow is expressed 
very accurately by the following empirical formula, based on the experi- 
ments of Professors Emswiler and Fessenden. Using the following 
symbols : 

pi = initial absolute pressure of the steam in pounds per square inch; 
p 2 = final absolute pressure of steam in pounds per square inch; 
a = area of the smallest section of the nozzle or orifice in square inches. 
Then the weight of the dry saturated steam discharged in pounds per 
second is approximately, 2 

w = ^ when p 2 is less than 0.58 pi (52) 

Now since in the theoretical formulas the weight discharged is inversely 
proportional to the square root of the specific volume v, or w is propor- 
tional toy— the formula above corrected for initial quality x of the 
steam is 

w = — ^— — 7- when p 2 is less than 0.58 pi. . . (54) 
60.5 v x 

When the steam is superheated the specific volume is considerably 
increased, and for this condition the author has found 'that the follow- 
ing equation gives very satisfactory results, 3 

Ihf Ji 

W 60.5 (1 + .00065 d) ' {55) 

1 Trans. A.S.M.E., vol. 28, page 483 and vol. 29, page 952. See also Bulletin No. 
76, Builder's Iron Foundry, Providence, R. I. 

2 A somewhat simpler formula, known as Napier's formula, which is accurate enough 
for most calculations, is the following: 

Pi a 

w = — when p 2 is less than 0.58 pi. (53) 

70 

3 For a more extended discussion of the flow of steam see The Steam Turbine, by 
the author, pages 52-57. 



190 



POWER PLANT TESTING 



when, as before, po is less than 0.58 pi and where d is the number of 
degrees (Fahrenheit) of superheat. 

When the final pressure p 2 is greater than 0.58 p x , the formulas must 
be modified to correspond to the reduced flow observed by inserting a 
coefficient K as a factor in the right-hand member of the equations. 
Values of this coefficient are most conveniently obtained from the 
curve in Fig. 232, which was plotted from the experimental results 
obtained by Professor Rateau. 

Formulas (52) to (55) are for the flow through nozzles with smooth 
walls, being well rounded at the entrance and the length along the axis 



1.0 


















































0.9 


































































$> 
































» a 0.8 














.1*; 
















































































•5 r° 

.2 ^ 0.7 

a 
























































< 


°> 
















































fj 










































« 8> 




















































f/ 












































y 












































IS °-4 




/ 
















































/ 














































|1" 




/ 














































/ 














CURVES FOR DISCHARGE OF STEAM 
MAINLY WHEN FINAL PRESSURE IS 






O (3 


/ 














?E 




/ 












GREATER THAN 58% OF INITIAL PRESSU 


0.1 


f 


















































































































































Fig. 232. — Rateau's Curve for Flow of Steam giving Values of the 
Coefficient K. 

at least three times the length of the shortest side or diameter. If the 
nozzles are of approximately rectangular section they must be made 
without well-defined edges; in other words the cross-section must show 
well-rounded corners. 

Orifice Measurements of the flow of steam are particularly recom- 
mended by some engineers for ascertaining the steam consumption of 
the " auxiliaries " in a power plant. This method commends itself 
particularly because of its simplicity and accuracy. It is best applied 
by inserting a plate J inch thick with an orifice one inch in diameter, 
with square edges, at its center, between the two halves of a pair of 
flanges on the pipe through which the steam passes. Accurately cali- 
brated steam gages are required on each side of the orifice to determine 
the loss of pressure. The weight of steam for the various differences of 
pressure may be determined by arranging the apparatus so that the 



FLOW OF FLUIDS 



191 



steam passing through the orifice will be discharged into a tank of water 
placed on a platform scales. The flow through this orifice in pounds of 
dry saturated steam per hour when the discharge pressure at the orifice is 
100 pounds by the gage is given by the following table: 1 



Pressure, Drop, 
Lbs. per Sq. In. 


Flow of Dry 

Steam per Hour, 

Lbs. 


Pressure, Drop, 
Lbs. per Sq. In. 


Flow of Dry 

Steam per Hour, 

Lbs. 


2 
1 

2 
3 
4 


430 

615 
930 
1200 
1400 


5 
10 
15 
20 


1560 
2180 
2640 
3050 



The Flow of Steam. Pitot Tube Meters are represented at their best 
in one of the types made by the General Electric Co. A nozzle plug (Fig. 
233) is inserted into the steam pipe and in this plug there are two sets of 
holes each communicating with a separate tube starting from the end 
of the plug. These pipes are connected separately to the unions in 
Fig. 234, showing the apparatus. The " leading " set of holes is subjected 
to velocity plus static pressure, while the trailing holes are subjected to 
velocity less static pressure only. The principles of operation are 
therefore the same as for the measurement of air by the Pitot tube 




Leading Set 

Fig. 233. — Nozzle Plug for Steam Meter. 

(see page 178). The part actuating the recorder consists of two cups 
connected by a hollow tube forming an elongated U-shaped vessel 
which is filled with mercury. This vessel is balanced on knife-edges. 
The cups are connected by flexible steel tubing to the unions shown 
at the top of the figure which are to be joined to pipes running to 
the nozzle plug. In the operation of the instrument the excess of 
pressure in the leading holes of the nozzle plug causes the mercury to 
shift its level and stand higher in the cup connected to the trailing holes. 
As a result of this unbalancing of weights the whole vessel will swing 
on the knife edges untii equilibrium is again established. A clock and 
drum device is provided for recording on charts the movement of the 
mercury vessel on its knife edges. Charts are graduated in pounds of 
steam per hour. Correction for variation of flow on account of fluctua- 

1 Journal A.S.M.E., Nov. 1912, page 1693. 



192 



POWER PLANT TESTING 



tion of pressure is automatic. This correction device is simply a Bour- 
don tube of a pressure gage connected to the recording device so that as 
the curvature of the tube changes to correspond with the pressure it 
shifts a small weight intended to adjust the pen. When superheated 



Balancing Weight 



Pressure and Temp. 
Correction Weight 




Fig. 234. —Steam Meter of Pitot Tube Type. 

steam is being measured temperature correction must be made by shift- 
ing the same weight by hand. 

The Burnham Steam Meter is one of the simplest types, and is 
serviceable only as an indicating instrument for 
" rough" measurements. The difference in level 
between the tip of the Pitot tube and the water 
in a gage glass is proportional to the flow of steam. 
The Pitot Tube used is shown in Fig. 225. 

The Orifice Steam Meter (Fig. 236) requires 
the insertion into the steam pipe of a special 
flanged fitting F in which there is an orifice as 
shown. Pressure difference between the two tubes 
ti and t 2 located in this flange (produced by veloc- 
ity) is measured by a differential mercury manom- 
eter. Without changing the orifice the apparatus 
is not adapted to a large range in the rate of flow. The spiral coils d 
and c 2 are inserted for maintaining by condensation constant water 




Fig. 236. —Orifice 
Steam Meter. 



FLOW OF FLUIDS 



193 



levels in each of the legs of the manometer, irrespective of variations of 
pressure. 

A variation of the orifice method has been applied very successfully 
on steam turbines of the few-stage type like the Curtis. The area of 
the nozzles between the second and third stages, and often also between 
the first and second stages, is invariable with the load if there is no over- 
load by-pass valve. The pressure drop is always great enough when 
steam is supplied at boiler pressure to make Napier's formula (page 
189) for the flow of steam applicable; that is, the weight of dry saturated 
steam passing through these nozzles of constant area is proportional to 
the pressure on the " inlet " side. If the area of the nozzles in one of 
these stages is known where the steam is approximately dry and satu- 
rated, and an ordinary recording pressure gage is attached to indicate 
the pressure on the " inlet " side of the nozzles, the weight of steam can 
be determined much more accurately than with any of the other auto- 
matic devices yet devised. If desired the chart of the recording gage 
can be readily graduated by a skillful draftsman to indicate directly 
pounds of dry steam. If the steam is superheated a correction curve 
can be readily made by applying the formula (55). 

Float Steam Meters are designed so that a float, usually a disk or a 
cone, moves against a constant resistance in a passage in which the un- 
restricted area for the flow of steam varies with 
the height of the float. This principle is applied 
in the St. John and Sargent meters in each of 
which there is a conical float connected to the 
registering device showing the rate of flow. In 
the St. John meter (Fig. 237) the float V rises 
with increased flow, carrying with it the arm N 
connected to the registering device. Accuracy 
of steam meters is usually not greater than ± 5 
per cent. 

Prices of steam meters: " G. E." Pitot tube 
$85 to $165 for indicating types, $260 to $270 
for recording types (General Eleetric Co., Sche- 
nectady, N. Y.); St. John Recorder $250 for 2- 
inch pipe, $550 for 6-inch pipe (G. C. St. John, 
New York); Sargent $200 for 2-inch pipe, $450 
for 6-inch pipe (Pittsburg Supply Co., Pittsburg, 
Pa.). 

The Flow of Water. When the quantity of water to be measured is 
not too large it is most accurately determined by weighing in tanks 
placed on scales, or by direct measurement of volume in calibrated 
tanks or barrels. Sometimes it is impracticable to weigh or measure the 




Fig. 237.— St. John Steam 
Meter. 



194 



POWER PLANT TESTING 



volume of the water directly, particularly when it must be measured 
under pressure. For measurements in pipes up to 2 or 3 inches in 
diameter a water meter is generally used. 

A great many types of water meters are sold commercially and not 
very many are accurate, so that it is absolutely necessary to calibrate 
them at least before and after a test, under the same conditions of tem- 
perature, pressure, and rate of flow. In many plants where meters are 

used constantly, suitable con- 
Dial nections are made to the dis- 

charge from the meter, so that 
at any time the flow through 
it can be diverted into a tank 
in which it can be measured 
by volume or weighed. 

One of the best types of 
water meters is illustrated in 
Fig. 238. This belongs to the 
class operating with a " pulsa- 
ting diaphragm." The inclined 
shaft S on this diaphragm trav- 
eling around in contact with 
the peg P on the plate B 
moves the counting mechanism 
through intermediate gears. 
This diaphragm in the Thom- 
son-Lambert meter (Fig. 239) 
is made of hard rubber reinforced with a steel plate, making it much 
more durable than those made without reinforcing. As the side cham- 
bers are alternately filled and emptied, the diaphragm is moved up and 
down with a kind of " pulsating " motion and operates the recording 
mechanism. The diaphragm divides the measuring chamber into two 
compartments of equal volume. While one of these is filling the other 
is emptying. For general purposes this type is probably used more 
than any other, and for a fairly constant flow is quite accurate; but 
because of leakage it is not accurate for rates of flow that at times have 
very low values. 

Piston Water Meter. The piston type of water meter (Fig. 240) 
is also used frequently. It belongs to the type operating in a cylin- 
der by a reciprocating piston which is driven backward and forward 
by the pressure of the water. In this device there are two pistons 
side by side. Water is admitted alternately at each end by a slide 
valve A moving on seats in the plate S, just above the bottom casting 
containing the inlet and outlet chambers. These valves are moved by 




238. — Pulsating Diaphragm Water Meter. 



FLOW OF FLUIDS 



195 




Fig. 239. — Thomson-Lambert Water Meter. 




Fig. 240. — Piston Water Meter. 



contact with the inner faces of the plunger heads near the end of the 
travel and move them over at the proper time. The lever L is moved 
back and forth by one of the plungers to operate the counting mecha- 
nism. The cored passages in the bottom casting are too complicated to 



196 



POWER PLANT TESTING 




Water Meter Operated by 
Velocity. 



be shown clearly. The plungers at the end of their travel strike against 
the rubber bumpers R, which are provided to reduce the shock. 

Meters actuated by the velocity of water are particularly suitable for 
measuring large quantities at low pressure. Fig. 241 shows an example of 

this class. Water flows into the wheel 
I after entering and passing through 
the screen S as shown by the arrows. 
Guide vanes deflect the water hori- 
zontally and radially outward from 
the center into the discharge passage 
A. The wheel when it revolves moves 
the counting mechanism G above. 
Objections to such meters are that 
they are very unreliable for small 
flows because of the friction of the 
parts, and an appreciable flow is required to start them. Friction is an 
important element in meters of this type, but they are not injured by 
moderately hot water. 

The readings of a water meter are usually in cubic feet. A water 
meter is essentially a water motor adapted for operating the gearing 
connected to the counting mechanism. 

Frequent calibrations of water meters are necessary because they are 
likely to become more or less clogged with dirt and refuse. The read- 
ings are also affected by the temperature, head, and quantity of water 
flowing, as well as by the amount of air carried in the water. A meter 
should always be calibrated at least at two or three rates of flow, as it 
scarcely ever happens that the conditions of the test are so uniform that 
the meter will be used only for a certain predetermined rate of flow. 1 

Willcox Water Meter. Automatic measuring devices are often used 
for determining the weight of condensed steam in engine tests or the 
weight of feed water in boiler trials. The Willcox meter 2 is a most satis- 
factory apparatus of this kind. It consists of a tank (Fig. 242) divided 
by a partition P into two compartments A and B, one above the other. 
The upper compartment A receives the inflow of water and the lower 
one B serves for measuring. Projecting into the lower compartment is 
a U-shaped discharge pipe C, which is always water-sealed. The upper 
end of the discharge pipe is covered by a bell float F, which is permitted a 
short, up-and-down movement. In the upper compartment there is a 



1 Calibration curves are usually plotted with meter readings as abscissas and actual 
volumes as ordinates. A curve should be plotted for each of the several rates of flow 
if they are different. Curves of meter readings (abscissas) and correction factors 
(ordinates) are also useful. 

2 Willcox Engineering Co., Saginaw, Mich. 



FLOW OF FLUIDS 



197 



short standpipe S, which is simply a hollow cylinder open at the top 
and bottom. The bell float F and the standpipe S are connected rigidly 
by a vertical rod (Fig. 243) so that they move together as one piece, and 
this is the only moving part in the apparatus. The lower end of this 
standpipe has a corrugated face, and when it is down in its lowest posi- 
tion its corrugated face rests on a soft seat or ring surrounding a circular 
opening in the partition P. This seat is made of a rubber composition 
which is not injured by boiling water. The apparatus can be used, 
therefore, with either hot or cold water without risk. 



Counter 



M Gage Glass 




Stand 
Pipe 




Fig. 242. — Willcox Water Weigher (by Volume). 



Fig. 243. — Bell Float. 



In the operation of the apparatus, when the standpipe S is down on 
its seat, water entering through the side inlet accumulates in the upper 
compartment A until it overflows the top of the standpipe. The 
water then flows down through the hollow standpipe into the lower 
compartment until there is a sufficient amount to seal the lower edge 
of the bell float F. Then as more water accumulates the bell float 
rises, lifting the standpipe S from its seat and the water in the upper 
compartment flows down into the lower one until the volume is that of a 
" unit charge " for the apparatus, when the " tripping " device dis- 
charges the water through the discharge pipe C. The " tripping " is 
accomplished by a " trip " pipe T, which is normally water-sealed, but 
which becomes unsealed when a " unit charge " has accumulated. 
While the water is accumulating in the lower compartment B the water 
in the left-hand leg of the " trip " pipe T is being slowly pushed down 



198 POWER PLANT TESTING 

because of the increasing pressure of the air under the bell float F, due 
to the increase of head of water, and a. corresponding amount of water 
spills over the upper end of the right-hand leg R of the " trip " pipe into 
the discharge pipe C. Due to this action the water level in T is lowered 
until it reaches the bend in the lower end of the " trip " pipe. Under 
these conditions the water column in R exactly balances the head of 
water in the lower compartment B and the air entrapped in the float 
valve F has a function similar to that of a scale beam, balancing on one 
side the head of water in the tank and on the other side the head of the 
standard water-column in R, which of course is always constant. At 
the instant this balance is secured a very small amount of water added 
in the lower compartment and the corresponding additional spill from 
R will destroy this equilibrium. Then the air compressed in the bell 
float F and the upper part of the discharge pipe breaks the water seal in 
R by suddenly discharging all the water in it. When the air pressure 
in the bell float F is thus reduced it drops down, carrying down with it 
the standpipe S in the upper compartment A. In this last operation the 
air is moved from the interior of the bell float F, and water flowing in 
to replace it will spill over the top of the discharge pipe C and will flow 
out at the other end until the lower chamber is emptied of the " unit 
charge." At this time the standpipe S becomes seated, due to the 
pressure of the water above the bell float and to the downward suction 
of the syphon. Thus the standpipe is held tightly upon its seat only 
at the instant when tightness is required; that is, while the " unit 
charge " is being discharged. After the standpipe has seated water 
again accumulates in the upper compartment A and the cycle of oper- 
ations is repeated. 

A mechanical counter shown at the side of the apparatus is connected 
to a ball float inside the lower compartment and registers the number of 
times the apparatus is tripped. An automatic device of this kind is 
easily calibrated by weighing several " unit charges," and it can then be 
used with, as great a degree of accuracy as can be expected with rapid 
weighings in tanks on platform scales. It may be expected to weigh 
hot or cold water with a maximum error of not more than one per cent 
for the conditions of calibration. ♦ 

Leinert (Worthington) Weigher. The apparatus shown in Fig. 244 
is one of the few devices made which actually weighs the liquid to be 
measured. It can therefore be used for liquids of widely varying den- 
sity without making corrections. It consists of a pair of open tanks 
supported on trunnions with knife-edge bearings (K) in such a way that 
when empty they assume the normal position as shown in the figure. 
After a certain quantity of liquid has entered the tank the counter- 
balancing effect of the lead weights in the casing W is overcome and the 



FLOW OF FLUIDS 



199 



tank tips over and the contents are siphoned out through the pipe P. 
By this tipping action the trough H receiving the liquid from the sup- 
ply pipe I is switched from the full to the empty tank, and at the same 
time the counter C is operated to 
register the number of times 
the tanks have been filled. Since 
weight is the method of measure- 
ment the record is independent of 
the temperature of the liquid; but 
there is always a very small vari- 
ation of weight with the rate of 
flow. The weight per charge can be 
adjusted by changing the number 
of weights in the casing W 1 , 

Venturi Meter. An arrange- 
ment of piping in which there is a 
gradual narrowing of the section 
to a minimum followed by a more gradual enlargement was invented by 
Mr. Clemens Herschel for measuring the flow of water. This apparatus 
is called a venturi meter and is shown in Fig. 245. Piesometer tubes 
(manometers) are arranged to indicate the pressure at the sections 
shown. Pressures at these sections will be denoted respectively by p m 
and p„. 




Fig. 244. — Tilting Tank Water Weigher. 



Pipes to Manometer 



J:£2==^=21= 



uu^** 



==! 



Fig. 245. — Herschel's Venturi Meter. 



From Bernouilli's theorem 2 it follows that the relation between the 
pressure in pounds per square foot and the velocities in feet per second 
at the two sections v m and v„ of a stream flowing through such a closed 
horizontal channel is given by 



+ 51 = 



+ 



2g 



(56) 



1 Henry R. Worthington, 115 Broadway, New York, and Holden & Brooke, London. 

2 See Jamieson's Applied Mechanics, vol. 2, page 458. 



200 POWER PLANT TESTING 

where 5 is the density of the water in pounds per cubic foot. If a repre- 
sents the area of a section in square feet, the volume of water flowing 
through any section, (cubic feet per second), is 



,v m = a„v„ = a„ / 2 gfo»-P» ) (57) 

With suitable manometers or with gages the pressures p m and p„ can be 
obtained, and since all other quantities can be represented by a constant 
k, we have 

Volume per Unit of Time = k (p m — p n ) . * . . . . (58) 

As usually made the venturi tube is merely a pipe which tapers from 
each end towards the throat, which is usually lined with 'hard bronze 
to secure a smooth bore and has a diameter of from \ to \ that of the 
pipe line. Its total length is about eight times the diameter of the pipe. 
In the commercial forms of this apparatus near the inlet or up-stream 
end and also at the throat are annular chambers encircling the tube, 
which communicate with the interior by numerous small vent holes. 
When no water is flowing in the venturi tube the pressure will be the 
same in these two annular chambers; but when there is a flow of water 
through it the throat pressure becomes less than the up-stream pressure. 
The difference between the two is proportional to the square of the 
velocity of the water. 

A recording device 1 has been arranged, consisting essentially of a 
large U-tube serving the same function as the one in the figure filled 
with mercury, supporting in each leg an iron float. These floats have 
toothed racks connected to their upper ends which engage with pinions 
on the same horizontal shaft with a cam. A small wheel supporting 
the recording pencil rides on the perimeter of this cam, which is ar- 
ranged so that the wheel rides on the greatest eccentricity of the cam and 
consequently the recording pencil will indicate on the chart the greatest 
flow when the rack is at its maximum height. The pipes connecting 
the U-tube with the venturi meter should always be full of water. Air 
cocks are provided for removing air that may accumulate in pockets. 2 
Since the flow is proportional to the square root of the difference of 
pressure a complicated cam device is required to permit the charts of 
the recorder to be made with equal divisions. 

The General Electric Flow Meter (see page 191) is also sometimes 
applied for measuring the flow of water in pipes. 

1 Builder's Iron Foundry, Providence, R. I. 

2 For more detailed discussion and tests see Herschel's papers in Trans. American 
Society of Civil Engineers, Nov., 1887 and Jan. 1888; also Power, Jan. 23, 1912. 



FLOW OF FLUIDS 



201 



Flow of Water through Orifices and Nozzles. Theoretically the veloc- 
ity of flowing water under any pressure is the same as the velocity at- 
tained by a body falling freely through a distance equal to that head 
(h) as in Fig. 247. Furthermore this statement would be the same 
even if the water had no free surface, provided, however, the pressure 
at the orifice was that due to a head h. If then there is no loss of head 
due to friction and eddies formed by the water passing through the 
orifice the velocity of discharge, v in feet per second, is 

v = vTgh, (59) 

where g 1 is the acceleration due to gravity and h is the head over the 
center of the orifice in feet. 





Fig. 247. — Discharge of Water from an Orifice. 

If a is the area of the cross-section of the orifice in square feet, q is 
the quantity or volume of water discharged in cubic feet per second, 
and assuming the stream is of the same cross-sectional area as the orifice, 

then q = aV2lh (60) 

Since the actual flow is less than the theoretical in most cases, and con- 
siderably less when the discharge is from a hole with sharp edges in a 
thin plate, a more general form may be written by inserting a suitable 
coefficient 2 of discharge k, then, 

q = ka V2gh (61) 

1 The value of g is approximately 32.2, so that equation (59) can be simplified into 
v = 8.02 Vh. 

2 This coefficient is often called the coefficient of contraction. 



202 



POWER PLANT TESTING 



For an orifice located in the side or bottom of a tank, consisting of a 
circular opening in a thin metal plate with a smooth sharp edge, the 
value of the coefficient k may be taken as 0.6 for all practical purposes. 
(See Report Power Test Committee of A.S.M.E. in Journal, Nov., 
1912, page 1829, and Hamilton Smith, Jr's, Hydraulics.) 

Calibration of Orifices and Nozzles. Water under a constant pressure 
is often measured by observations of the flow through either orifices or 
short nozzles which have been carefully calibrated. The apparatus re- 
quired for this calibration consists usually of a suitably arranged stand- 
pipe to which the orifice or nozzle can be attached so that a given head 
of water can be maintained 1 and barrels on scales (or a tank calibrated 
for volumes) to receive the water discharged. 

A pressure of one pound per square inch is equivalent to a head of 
water at 62 degrees Fahrenheit of 27.72 inches, or 2.31 feet. A normal 
atmospheric pressure (14.7 pounds per square inch) is therefore equiv- 
alent to a head of 33.96 feet of water. Then for a given pressure or 
head the quantity of water discharged in a given time is readily obtained 
and the coefficient of discharge can be computed by substituting the 
values of quantity of discharge q, the head h, and the area a, in formula 
(61). 

Data and results should be tabulated in the form given below. The 
relative roughness of the edge of the orifice or of the inside surface of 
the nozzle should be recorded. 

FLOW OF WATER 

Flow of water through a 

Date Observers 

Form of orifice or nozzle Formula Diameter, feet 

(Sketch) Area, square feet 



No. of 
Reading. 


Head in 
Feet. 


Time in 
Seconds. 


Total 
Pounds or 
Cu. Feet. 


Pounds per 
Second. 


Cu. Feet 

per 
Second. 


Coefficient of 

Discharge 

(k). 


Remarks. 


















Average 

















1 In many places a suitable pressure tank is not available, and in such cases the cali- 
bration can be made by attaching the orifices or nozzles to pipes carrying water under 
pressure. The readings of the pressure gage can be reduced to the equivalent head in 
feet, to which must be added, if the center of the gage is higher than the orifice or nozzle, 
the distance in feet from the center of the nozzle to the center of the gage. 



FLOW OF FLUIDS 



203 



Curves. Curves should be plotted for each orifice or nozzle with 
head in feet for abscissas and (1) the discharge (cubic feet per second) 
and (2) the coefficient of discharge for ordinates. 

Flow of Water over Weirs. When large quantities of water are to 
be measured, then orifices are unsuitable and it is customary to pass the 
whole body of water over a weir or gage notch. This consists of a 
board placed across the stream so that all the water 
must pass over it. The length of the notch is usually 
made less than the width of the stream to give definite 
conditions. This is accomplished most easily by sawing 
the notch out of a long board and beveling the edges. 

A typical arrangement for measuring the head of 
water on a weir is illustrated in Fig. 248. The head 
must be determined with great accuracy, and this is 
done usually by means of a hook-gage, Fig. 249, and a 
suitable machinist's or carpenter's level. 




Fig. 248. — A Weir for Measuring Water. 



Fig. 249.— A Hook 
Gage. 



The hook-gage consists of a sharp-pointed hook H, attached to a 
vernier scale V, intended to measure very accurately the amount the 
hook is moved. Before taking an observation the hook must first be 
submerged and then raised slowly till the point just breaks the surface 
of the water. The correct height of the surface is obtained at the in- 
stant when the point of the hook pierces it. The head h of the water 
flowing over the weir (Fig. 248) is obtained by setting by means of a 
straight-edge SE and the level L the point of the hook at the same 
level as the crest of the weir. The height observed in this position is 
called the zero head. It is to be subtracted from all other readings to 
get the head of water flowing. The hook-gage must be placed in such 
a position on the upstream side of the weir where the surface has no 



204 



POWER PLANT TESTING 



appreciable velocity and where there is very little disturbance due to 
eddies. In terms of the following symbols, 

q = quantity or volume of water discharged in cubic feet per second; 
h = the head in feet on weir measured in still water; 
b = breadth of the weir in feet; 
n = the number of contractions; 
k = coefficient of discharge. 

q = 2/3 kh % (b — 0.1 nh) Wg 



..... (62) 

This is the well-known Francis formula for a rectangular notch. The 
ordinary rectangular notch has two contractions, one at each side of 
the crest. Triangular notches in weirs are sometimes used. One 
of these in the form of a right-angled isosceles triangle is shown in Fig. 
250. It has the advantage of giving the same form of stream what- 




Fig. 250. — Weir with a Triangular Notch. 

ever the size of the notch or the height of water passing through. It is, 
therefore, particularly suitable for measuring a flow of water which is 
somewhat variable The quantity of water discharged over a triangular 
weir or notch is 

q = 4/15 kbh% V2g. (63) 

When the angle is 90 degrees, 

b = 2 h and q = 4.26 kh % . . . 
Also when the angle is 60 degrees, 

b = 2 h tan 30 and q = 2.47 kh%. 



. . . (64) 
. • • (65) 



FLOW OF FLUIDS 



205 



3. Weir Meters. A weir or notch will measure any quantity of 
water if made of a suitable size. Rectangular weirs are generally used 
for large quantities and notches of various shapes for small quantities. 
For accurate work the head on the crest is measured with a hook-gage 
but in many cases a float is used. The instrument used for measuring 
the head should not be less than two feet from the crest and preferably 
farther away. The distance of the crest from the bottom of the weir 
tank should be not less than three times the average head. For a weir 
with two contractions the width of the tank should be not less than 
three times the width of the weir. To maintain the surface free from 
ripples baffle plates, preferably of perforated sheet metal, should be 
located between the supply pipe and the instrument for measuring the 
head. 

Lea's Recorder 1 for V-notch Weirs is successfully used in many 
services for measuring water. Water level is measured by a sheet- 
metal float usually about 12 inches 

in diameter which is attached to the 

vertical shaft S of the recorder in 

Fig. 251. On the upper end of this 

shaft is a rack R meshing with a 

pinion on the left-hand end of the 

horizontal shaft carrying the drum D 

which has on its curved surface a 

spiral band over which a trailing- 

arm F is fitted. The] curvature of 

the spiral band has been made to 

conform to a logarithmic curve so 

that increments of movement of the 

trailing-arm are proportional to the 

quantity of water flowing, and not 

to the up and down movement of the float. The trailer F is connected 

to the pen-arm P, making a record on the paper drum C. These charts 

will therefore have equally spaced ordinates and the area under the 

curve traced on them is proportional to the quantity of water flowing in 

a given time. 

Mover's Recorder (Fig. 252) consists of a weir tank T into which 
water discharges through the supply pipe S. A float F is located un- 
der the recorder R. The vertical shaft of the float, held in line by small 
ball-bearing guides, is connected to the pen point P directly, without any 
intervening gears or linkages. Baffle plates B are placed between the 
supply-pipe and the float to eliminate ripples and steady the float. 
The notch N follows almost exactly the theoretical lines for a flow pro- 
1 Yarnall-Waring Co., Chestnut Hill, Pa. 




Fig. 251. — Lea's Recorder. 



206 



POWER PLANT TESTING 




Fig. 252. — Moyer's Recording Weir. 



portional to the head, accurate allowances being made also for end 
contractions. Radial ordinates traced by the pen point P are there- 
fore proportional to the rate of flow. By measuring these charts with 

a Bristol-Durland averager 
for circular charts (see page 
87) the quantity of water 
flowing in a given time can 
be accurately obtained. 

The charts are graduated 
in pounds of water per hour 
jinstead of cubic feet. This 
is made possible by the au- 
tomatic temperature correc- 
tion of this apparatus. For 
a given weight of flow as 
the temperature increases 
or decreases the head in- 
creases or decreases corres- 
pondingly and vice versa; 
but at the same time the 
displacement of the float in- 
creases as the water becomes, lighter by reason of being hotter. These 
two influences therefore counterbalance, making the weight discharged 
in a given time proportional to the ordi- 
nates of the curve traced by the pen of 
the recorder. This apparatus is accu- 
rate to | per cent for temperature cor- 
rection. 

An automatic float valve is provided 
for shutting off the water supply to pre- 
vent overflowing. 

Lea's Recorder indicates also pounds 
per hour, but because the movement of 
the float is not proportional to the head 
the automatic correction for temperature 
is only an approximation. 

No weir device is very accurate for 
very low rates of flow. Any mistake 
made in determining h will produce a 
larger percentage error in the results 
with the rectangular and triangular 
notches than with an orifice. Where great accuracy is desired and the 
quantity of water to be handled is not too large, an orifice calibrated 




Fig. 253. — Best Kind of Orifice 
for Engine Tests. 



FLOW OF FLUIDS 207 

and used in the bottom of the tank as shown in Fig. 253 is to be pre- 
ferred to measurements with a weir. This remark is particularly appli- 
cable in connection with the measurements of cooling (circulating) water 
in tests of large steam engines and turbines. 

Calibration Data Sheets. Use the same form for data as given for 
calibration of orifices or nozzles on page 202. 

Curves should be plotted with heads for abscissas and (1) the 
discharge (cubic feet per second) and (2) the coefficient of discharge for 
ordinates. 

Weighing Liquids in Tanks. In order to weigh liquids under a con- 
tinuous' flow two tanks, usually made of sheet metal, are generally used. 
Each tank is placed on a scales and the liquid is alternately discharged 
into each. The discharge pipe is usually arranged so that it is movable 
from one tank to* the other by turning on a screw thread. At the side 
of each tank near the bottom a so-called " quick opening " valve or cock 
is provided for rapidly emptying the tanks. These discharge valves 
should be large, because the more rapidly the tanks can be emptied 
the greater the quantity of water the arrangement will handle. 1 

When only one platform scales is available an arrangement like that 
shown in Fig. 254 can be used efficiently. The larger tank is placed on 
the scales and the smaller one is supported on a platform or bench at 
such a height that it can be readily discharged into the larger tank. 
During the operation of weighing and emptying the larger tank, the 
liquid is discharging into the smaller one; and when the discharge is 
again directed into the larger tank the valve or cock on the smaller one 
is opened so that its contents will be included in the next weighing of 
the larger tank. 

For weighing feed-water in boiler tests the reverse of this arrange- 
ment is frequently applied. There are as before two tanks or barrels, 
of these the one more elevated is on a platform scales, and the attendant 
doing the weighing empties weighed quantities of water into the lower 
tank as needed to supply the feed-pump. In the lower tank the water 
level must be the same level at the end as at the beginning of a test. 2 

-In cases where the flow is absolutely constant as in the discharge of 
water from nozzles or orifices with a constant head a tank may be filled 
at intervals, observing accurately the time for filling with a stop-watch 
and weighing each time. The average of several such determinations 
gives a fairly accurate result. 

1 The discharge can be increased by attaching a short pipe to the discharge side 
of the valve which by reducing the contraction increases the flow. 

2 For determining these levels in the tank a water-gage glass is very convenient. 
If, however, there is no gage glass on the tank marks can be made with a knife-scratch 
or by painting a line on the inside of the tank. 



208 



POWER PLANT TESTING 



Liquids are also often measured instead of weighed in calibrated 
tanks. In every case the temperature of the liquid must then be ob- 
served. In some cases the tanks have graduated scales at the side of a 
glass water gage from which the volume of water can be observed; or again 
there is only a single mark up to which the tank is to be filled each time. 
Establishing the exact level for a large surface is not an easy matter 
and to make this method more accurate the marks up to which the 
tank is to be filled are preferably put on a portion of the tank at the 
top which has been made considerably smaller in size than the rest of 
the tank. 

It is a very poor method to fill tanks up to the rim on account of the 
variableness of the meniscus which may vary from various causes. 



ife 



J^Quick Jt 

pT\ Opening" LJ-\J- 



m 




Fig. 254. — Weighing Device. 



Fig. 255. — "Double" Tank. 



Actual weights corresponding to measurements of volume are always 
varying with the temperature of both the liquid and of the tank or 
collecting vessel. It is therefore necessary in every case to determine 
by actual tests the weight corresponding to the volume of a tank for a 
given liquid at various temperatures and apply a calibration curve for 
temperature variations to all measurements. Calibrations should be 
made also with the inside wetted surface in as nearly the same condition 
as it will be after each emptying in a test. 

An ingenious method of measuring the flow of a liquid is illustrated 
in Fig. 255. It shows a tank separated by a partition into two parts. 
The partition is not quite as high as the sides of the tank. In oper- 
ation one of the halves is filled up to the top of the partition, permitting 
any excess to flow over into the other half. Then the supply pipe is 
swung over to the second half which is filling while the first half is being 
emptied. The tanks must be emptied, of course, more rapidly than 
they are filled. 



FLOW OF FLUIDS 209 

In order to make easier the supervision and checking of tests it is 
desirable that as nearly as possible equal quantities should be weighed 
or measured as the case may be. 

Automatic scales provided with a continuously operating controlling 
device have been successfully developed. The poise on the weighing- 
beam is set in motion when the article to be weighed is put on the scales 
and when the beam shows it is balanced it stops automatically. The 
weight is usually registered by means of a counting device but a printing 
recorder can also be used. 



CHAPTER VIII 
CALORIFIC VALUE OF FUELS — SOLID, LIQUID AND GAS 

Calorific power is a term applied to the quantity of heat generated 
by the complete combustion of a definite quantity of fuel. In order to 
insure rapid and complete combustion the fuel is preferably burned in 
an atmosphere of oxygen under pressure. This calorific power of fuels 
is expressed in the English system as British thermal units per pound, 
and in the metric system as calories per kilogram. 

In fuel calorimetry it is always assumed in engineering calcula- 
tions that at about the usual " room " temperatures the specific heat of 
water is constant, so that the weight of reasonably pure or distilled 
water in pounds times the change in temperature in degrees Fahrenheit 
is the heat change in British thermal units (B.t.u.). Similarly the 
weight of water in kilograms times the change of temperature in Centi- 
grade degrees is the heat change in kilogram-calories (French) or Warme 
Einheiten (German). For conversion constants see page 29. 

The quantity of heat generated by combustion is measured by the 
rise in temperature of a given weight of water in a calorimeter of which 
the cooling effect or water equivalent k has been determined, and the 
temperature of any gas escaping has been reduced to that of the room. 
Now if 

W/ = weight of the fuel in pounds, 
w w = weight of the water in pounds, 
k = water equivalent 1 of the calorimeter, in pounds, 
ti = initial temperature of water, degrees Fahrenheit, 
t 2 = final temperature of water, degrees Fahrenheit, 
Q = total heat generated, B.t.u. 

1 Water equivalent is used to express the heat-absorbing effect of the calorimeter 
as equivalent to that of a weight of water. This may be found (1) as for calorime- 
ters used for determining the quality of steam by the hot-water method (see page 72) 
(2) by taking the sum of the products of the weights and specific heats of the various 
parts of the calorimeter (see Calorific Power of Fuels, by H. Poole, pages 14 and 15), or (3) 
by comparing the results obtained with those that should have been secured, if there 
had been no absorption of heat, by the combustion in oxygen gas of some substance 
of which the heat value is known; as, for example, pure sucrose, carbon, napthalene, 
or benzoic acid. Samples of the materials of which the heat value has been worked 
out very accurately may be obtained together with a certificate at a very small ex- 
pense from the U. S. Bureau of Standards, Washington, D. C. The standard sample 

210 



CALORIFIC VALUE OF FUELS 



211 



H = 



(68) 



then the calorific value H per pound of fuel in British thermal units is 
Q _ (w B + k) (t 2 - ti) 

W/ W/ 

Corrections for Radiation can be practically eliminated by having the 
temperature of the water in the calorimeter before ignition as much 
below the " room " temperature as the final temperature is above. 

Bomb Calorimeters. Formerly the calorimeters used for burning 
fuels in an atmosphere of oxygen were arranged for combustion at con- 
stant pressure, but since it was found that more reliable results could be 
obtained generally with apparatus maintaining a constant volume, the 
former type is not now much used. When the combustion takes place 
at constant volume, the vessel receiving the charge 
of fuel and oxygen must be designed to withstand 
a great pressure, and therefore on account of the 
massive construction required the vessel is called 
a bomb calorimeter. The essential part of such a 
calorimeter is the strong steel vessel or bomb simi- 
lar to Fig. 256. It consists essentially of a steel 
shell S having a capacity of about 50 cubic inches 
and capable of resisting with safety a pressure of 
about 750 pounds per square inch. This shell is 
usually provided with a coat of enamel or a lining 
of platinum or nickel on the inside and is nickel- 
plated on the outside. The coating or lining on 
the inside is intended to resist corrosion and oxi- 
dizing action during the combustion. The advan- 
tage of the nickel lining over the coat of enamel 
is that when it is worn out or broken it can readily 
be replaced and at much less expense than the en- 
amel. The shell is closed at the top by an iron cover or cap which is to 
be made tight by screwing down on a lead washer with considerable 
force, using a long wrench. At the top of this cover or cap there is a 
conical seated valve, which is screwed in through the gland and stuffing- 
box G, by attaching a wrench at P. The valve and its seat are made of 
good nickel, as this metal is not easily oxidized. A wire electrode B, 
which is well insulated from the cover, extends into the shell and con- 
should be made into a pellet (see page 216) weighing about 1.5 grams which imme- 
diately after weighing should be put into the calorimeter and burned in commer- 
cially pure oxygen gas at about 400 pounds per square inch. After correction for 
radiation (see page 214) the discrepancy in the heat balance is the product of the re- 
quired water equivalent (pounds) and the observed temperature range. Detailed 
directions for very accurate determinations are given in Circular No. 11, of U. S. Bureau 
of Standards. 




^VV^^vVxVX^ 



Fig. 256.— Section of 
Bomb Calorimeter. 



212 



POWER PLANT TESTING 



ducts the electric current for firing the charge of fuel, which is placed 
©n a platinum dish or crucible supported by another wire A, attached 
to the cover on the inside. 

Usually one gram of finely powdered coal which will pass through a 
sieve having 100 meshes to the inch (" 10,000 meshes to the square 
inch ") is put into the dish to make a test for calorific value. 1 A small 
iron wire (which was previously weighed) is then suspended over the 
dish between the electrode and the wire support for the dish. The 
cover should then be screwed on with a long wrench, the shell itself 
being held in a vise. The complete Mahler apparatus 2 is shown in 
Fig. 257, showing the cylinder of oxygen O, the pressure gage M, the 
calorimeter vessel D. The end of the conical-seated valve (Fig. 256) is: 




Fig. 257. — Complete Mahler Apparatus. 



attached by means of pipe connections, preferably flexible, to the union 
U and to the valve W, which because of the high pressure should be 
opened slowly and carefully, and allow sufficient oxygen to pass into 
the bomb to provide a considerable excess above that actually required. 

1 The Power Test Committee of A.S.M.E. recommended that the sample should 
be " air dried" (see page 232); and that a similar "air dried" sample should be tested 
for moisture, so that the final result may be based on heat value per pound dry coal. 
Many chemists and engineers prefer to use a sample of coal powdered "as received" 
and determine the heat value per pound "as received." The latter method does not 
give as accurate results as the former, but slightly reduces the time required for making 
the calorific determination. 

2 The Mahler type of calorimeter is recognized as the most complete and accurate 
apparatus of its kind. Where the engineer does not have this instrument or some 
other reliable calorimeter of similar construction, the heat units can be determined by 
sending samples to a testing laboratory where such instruments are used." — Report 
of Power Test Committee of A.S.M.E. in Journal, Nov., 1912, page 1698. 



CALORIFIC VALVE OF FUELS 213 

The' pipes for connecting the bomb to the oxygen cylinder should connect 
also with a pressure gage as shown, so that the pressure in the bomb can 
be regulated. For the combustion of coal a sufficient volume of oxygen 
is admitted to Mahler bombs of the usual size to make the pressure in 
the bomb from 350 to 375 pounds per square inch. Now close the 
valve on the oxygen cylinder and the conical-seated valve on the bomb, 
removing also the connections between the bomb and the oxygen cylin- 
der. Oxygen should be admitted to the bomb slowly, because if acci- 
dentally the oxygen be allowed to go in a little too rapidly, some of 
the sample of coal will be blown out of the dish and will probably not 
be burned. The bomb should then be placed in the calorimeter vessel 
D, which should be filled with a quantity of water previously weighed 
(at least about five pounds) to fill it to about the level indicated in the 
figure. Place the calorimeter thermometer T into the vessel, being 
careful that the end will not be touched and broken by the stirrer or 
other parts, and then after agitating the water for a few minutes to 
establish a uniform temperature, the observations can begin. The 
temperature should be very carefully observed for five minutes and 
recorded minute by minute, to determine the rate of variation of temper- 
ature before combustion. Then the electric circuit should be made 
and the combustion will, of course, begin immediately; but some little 
time will be required for the transmission of the heat generated to this 
water. Now take the temperature at the end of a half minute after 
making the electric circuit, and continue observing the temperature 
every half minute until it reaches its maximum value and begins to fall 
off regularly. Continue the observations for five minutes more to 
determine the rate of the fall of the temperature. The stirrer should be 
worked continuously but not too rapidly throughout the test, being 
careful, however, that the thermometer is not broken. When the 
observations have been finished, the conical-seated valve should be 
opened first to relieve the pressure and then the cover or cap can be 
unscrewed and removed. 1 • 

The method described for the use of the Mahler bomb calorimeter 
can be applied also for determinations of calorific value of liquid fuels. 
Heavy oils can be weighed directly in the platinum dish or crucible, 
but light oils which are easily vaporized must be put into specially 
prepared glass bulbs which are broken to allow access of the oxygen, 

1 Some engineers wash out the inside of the bomb with a little distilled, water to 
collect the nitric and sulphuric acids formed. Usually, however, this correction for 
acids is not made, as the heat liberated in the formation of the acids is usually less than 
one-third of one per cent, which, of course, would be subtracted from the calorific 
value obtained. If the reader is interested he will find the method explained with the 
necessary data in the Calorific Power of Fuels, by H. Poole, page 62. 



214 POWER PLANT TESTING 

just before the cover is put on the bomb. If sufficient oxygen is pro- 
vided in every case there will be complete combustion in the calorimeter 
with no other refuse than the cinders remaining. 

A specimen calculation is given below: 

Weights, — coal, .0030 lb.; 1 water in calorimeter, 4.85 lbs.; water 
equivalent of bomb, etc., 1.10 lbs. Weight of iron wire, .0002 lb. 

Preliminary Observations. 

Beginning 60.23° F., 3 minutes, 60.26° F., 

1 minute, 60.24° F., 4 minutes, 60.27° F., 

2 minutes, 60.25° F., 5 minutes, 60.28° F. 

„ , , . .. , , . .. 60.28-60.23 mo ' 

Rate of variation before combustion a = = = .01 F. 

5 

Observations during Combustion. 

6 minutes, 65.45° F., 

7 minutes, 67.29° F., 

8 minutes, 67.38° F., max. 2 

Observations after Maximum was reached. 

9 minutes, 67.34° F., 12 minutes, 67.28° F., 

10 minutes, 67.32° F., 13 minutes, 67.27° F. 

11 minutes, 67.30° F., 

t, . , . • .. - + • 67.38 - 67.27 AOOO _ 

Kate of variation alter maximum a m = = = .022 h . 

5 

The rate of variation of temperature before combustion was for cool- 
ing the water and that after combustion was for a loss of temperature 
by the water. Evidently, then, the two rates are opposed in effect and 
the true average rate of variation is 

a „ = ~ - 01 + - 022 = _j_ -006 o F per minute> 

Three minutes (5-6, 6-7, and 7-8) were required for complete com- 
bustion or for the water to reach the maximum temperature. Total 
cooling correction to be added to the observed rise in temperature is, 
therefore, 3 X .006 = .018° F. 

1 The coal had been warmed for one hour at a temperature of from 240 to 280 
degrees Fahrenheit before weighing, in a crucible over a Bunsen burner or an alcohol 
lamp to drive off the moisture. In the best modern practice determinations are made 
on the basis of dry coal. 

2 Some engineers make a curve of temperatures (ordinates) and time (abscissas) 
and use for the final temperatures in the calculations the value from the curve, when 
the part of the curve representing the cooling becomes a straight line. The difference 
in numerical values by the two methods is usually very slight. 



CALORIFIC VALUE OF FUELS 



215 



The total rise as corrected is 7.10 + .018 = 7.118° F. 
The quantity of heat generated is, therefore, Q = (4.85 + 1.10) 
X 7.118 = 42.35 (B.t.u.) for .0030 lb. of coal: and from this result 



&* 



- _:_t:: ._: 



y////////?////z/z/////s//, 



a 





MS/MS/M/ft 



Fig. 258. — Atwater's Fuel Calorimeter. 




Fig. 259. — Emerson's Fuel 
Calorimeter. 



must be subtracted the heat of combustion of the iron wire .0002 X 3000 1 
or 0.60 B.t.u. The net value of the heat generated from the coal is, 
therefore, 42.35 - .60 = 41.75 B.t.u. 

A modification of the Mahler bomb calorimeter has been designed 

1 The calorific value of pure iron is about 3000 B.t.u. per pound, and iron wire No. 
34 B. & S. gage one inch long will generate in combustion .63 B.t.u. This is the size of 
wire generally used in calorimeter work. 



216 



POWER PLANT TESTING 



2LX 



a 



'!£. 



by Atwater, 1 Fig. 258, and another by Emerson, Fig. 259. The former 

consists of the shell of the bomb A, the cap C screwed on numerous 

threads to the shell, and holding down the cover B. Into the vertical 

neck of this cover a screw E, holding another screw F, is fitted and is to 

rmmj. p-™i be turned down tightly, a lead washer serving 

^ ^ . as " packing." A small passage for the ad- 

mission of oxygen from G is opened and closed 
as required by turning the screw F operating 
a needle-valve. A wire H of platinum or other 
non-oxidizable metal passes through the cover 
B and is insulated from it by a collar of hard 
rubber. Another wire rod I is attached to 
the lower side of the cover and electrical con- 
nection is made between the two wires H and 
I by a small iron wire stretched between them. 
A platinum crucible provided for receiving the 
fuel is supported by a " screw " ring. Ball 
bearings of hard steel are sometimes placed 
between the cover and the cap to reduce fric- 
tion when screwing down. Holes located in 
the sides of the cap are for the attachment of 
a long spanner wrench when turning down the 
cap. A hand-stirring device S is used for 
agitating the water in the vessel Q. 
The usual arrangement of the oxygen tank, pressure gage and tubing 

for charging a bomb calorimeter is illustrated in Fig. 260. A pellet 

press for compressing samples of fuel into a suitable size to burn in 

the crucible of this calorimeter is 

shown in Fig. 261. 

Fig. 259 shows another form of 

bomb calorimeter (Emerson) of 

which the Mahler is typical. It 

consists of a nearly spherical shell 

S, divided into two parts which are 

screwed together by the ring R. 

Powdered fuel is placed in the cm- 

cible C and is ignited electrically FiG m _ A pdIet Pregs for Compress . 

by the current passing through the ing Samples of Fuel. 

water in the vessel Q from the 

terminal at A, then through an insulated contact point P in the bottom 

of the calorimeter to a small platinum or iron wire in the crucible C, 

which becomes heated by the passage of the current to a white heat, 
1 Atwater, Bulletin No. 21, U. S. Dept. of Agriculture. 



Fig. 260. — Apparatus for 
Charging a Bomb Calo- 
rimeter with Oxygen. 




CALORIFIC VALVE OF FUELS 



217 



igniting the fuel. One end of this small wire is fastened to make elec- 
trical contact with the lining of the calorimeter, which in turn is con- 
nected electrically with the plug and terminal at B. 

The outer vessel O is to be filled with water to the top. The stirring 
device consists of small propellers F, on a vertical shaft operated by a 
small electric motor M. 




Fig. 262. 



- Typical Parr Calo- 
rimeter. 



Fig. 263. — Parr 
Bomb for Hot 
Tube Ignition. 



Fig. 264. — Parr 
Bomb for Elec- 
trical Ignition. 



Parr Calorimeter. It is not always convenient to secure a supply 
of oxygen under pressure for use in a Mahler bomb, and consequently 
another type of fuel calorimeter, known as Parr's using a chemical 
(sodium peroxide) as the source of oxygen, has found considerable use, 
especially for relative determinations in power plants. The results 
obtained can scarcely be depended on to be as accurate as determina- 



218 



POWER PLANT TESTING 



tions with one of the bomb type. 1 Fig. 262 illustrates a simple form of 
Parr calorimeter. Sectional views of the two kinds of calorimeter 
vessels used are shown in Figs. 263 and 264. In the former the ignition 
is accomplished by dropping a hot wire through the neck into the shell A 
of the calorimeter. The cover is attached to the shell by means of a 
threaded nut F. A charge for the bomb consists of about .002 to .004 
pound of pulverized coal from which the moisture has been driven off by 
warming for about an hour at a temperature of about 240 to 280 degrees 




Parr Calorimeter with Motor Stirring Device. 



Fahrenheit, and eighteen times as much by weight of sodium peroxide, 
which supplies the oxygen needed for combustion. Reactions pro- 
duced by combustion are complex as the products of combustion C0 2 , 
H 2 0, S0 2 , S0 3 , etc., combine with some of the Na 2 2 or Na 2 to 
form Na 2 C0 3 , NaOH, Na 2 S0 4 , etc. The charge should be well mixed 

1 As regards the accuracy of the determinations very much depends on the chemi- 
cal purity and dryness of the sodium peroxide. If it is absolutely pure and the 
apparatus is handled with skill, it is easily possible to get results comparable with the 
bomb types. 



CALORIFIC VALUE OF FUELS 219 

by shaking the shell after the cover has been securely fastened. The 
cover must be attached very securely by turning up the nut with a long 
wrench while the shell is held in a vise or in some similar manner, because 
there is a violent explosion when ignition takes place. When the hot 
wire (Fig. 263) is put into the tube in the long neck L, the cap R at the 
top must be struck quickly with a mallet in order to open the valve M, 
which opens inward into the shell and permits the wire to fall through 
before it cools. To be certain of obtaining a good result the wire 
should be heated almost to a white heat, and the coal should preferably 
be put into the shell after the sodium peroxide. The rise of the mercury 
in the thermometer will indicate when an explosion has occurred. 

The calorimeter is provided usually with wings or small propeller 
blades for agitating the water in the vessel O. The small pulley P 
(Fig. 262) shown at the top of the neck is used for turning the calorimeter 
bodily in the water when supported on the pivot F, shown at the bottom 
of the figure. The water equivalent of the calorimeter is determined 
in the same way as for other fuel calorimeters. Fig. 265 shows the Parr 
calorimeter as designed for electrical ignition and with a stirring device 
operated by an electric motor. 

Allowance must be made in the calculations for the heat generated by 
the chemical reactions of the sodium peroxide, which for the proportions 
given for a charge is approximately 27 per cent of the heat generated. 

Example Illustrating Calorific Determination with Parr Calorimeter. 
Weight of powdered coal .00401b., containing 1.3 per cent moisture, 
and 6.7 per cent ash. 

Weight of sodium peroxide .072 lb. 

Weight of water 7.160 lbs. 

Water equivalent of bomb 0.253 lb. 

Total equivalent weight of water 7.413 lbs. 

Temperature rise 10.2°F. 

Total heat generated, 

7.413X10.2 = 75.61 B.t.u. 

Heat due to combustion of Iron Wire (see page 215) 1.11 B.t.u. 
Heat due to coal alone, 

(75.61 - 1.11) (1.00 - .27) = 54.39 B.t.u. 

Heat value per lb. coal as fired, 

^a>- 13,598 B.t.u. 

Heat value per lb. dry coal, 

13,598 , n _„„ t-. , 
"igr- 18,780 B.tu. 

Heat value per lb. combustible, 

13,780 ., . «<->/-> t-« i 
-^3- = 14,780 B.t.u. 



220 



POWER PLANT TESTING 



Carpenter's Calorimeter. There are few calorimeters in which the 
oxygen is supplied at constant pressure which are altogether successful. 
One of the best forms of an apparatus of this kind has been designed by 
Carpenter, especially for coal determinations. With this apparatus no 
thermometers are needed, as the rise in temperature is measured by the 
expansion of the mass of water surrounding the combustion chamber. 

This apparatus is shown in Fig. 266. It consists of a combustion 
chamber 15, provided with a removable bottom 17, through which the 
tube 23, supplying the oxygen, passes into the combustion chamber. 

Electric current for ignition is con- 
ducted through the wires 26 and 
27. The removable bottom sup- 
ports also the asbestos cup or 
crucible 22, used for holding the 
sample of coal to be burned. Just 
beneath the crucibles a silver mir- 
ror 38 is provided to " deflect " the 
heat. The plug containing the wires 
and the oxygen pipe 23 is made of 
alternate layers of asbestos and vul- 
canite. Products of combustion 
leave the combustion chamber 
through a spiral tube, the parts of 
which are marked 28, 29, 30, and 
31, into the small vessel 39, at- 
tached to the outer casing of the 
instrument, and are finally dis- 
charged into the air from a small 
hole 41 in the side of the vessel. 
The pressure in the chamber 39 is 
indicated by a manometer gage 40. 
The inner casing of the instrument 
1, containing the water for absorb- 
ing the heat generated, is nickel- 
plated and highly polished to re- 
duce radiation as much as possible. 
An open glass water gage 10 passes through the casings and extends 
below the water level. This water gage, with the scale attached to it, 
replaces the thermometer used in other calorimeters for measuring the 
rise in temperature. The scale is graduated to read inches, and it is 
calibrated usually by burning coke in the calorimeter, and determining 
thus the rise of the water level for a determinable weight of pure carbon. 
A calibration curve is usually supplied with the instrument. By mov- 




Fig. 266. — Carpenter's Calorimeter. 



CALORIFIC VALUE OF FUELS 221 

ing the diaphragm 12, by means of the screw 14, the water level can 
be regulated, as well as the " zero " level in the glass water gage 10. A 
funnel 37 is provided for filling the instrument, and by inverting it, 
this funnel can be used also for draining. The instrument holds 5 
pounds of water, and 2 grams of coal is the amount taken usually for a 
charge, requiring about twenty minutes for complete combustion of 
powdered coal. The asbestos cup 22 should be heated in the flame 
of a Bunsen burner before it is weighed. The charge of dried coal 
should then be put into it and weighed again. The difference will be 
the weight of the coal used. Now put the charge into the combustion 
chamber 15, place the platinum ignition wire above the coal, connect 
wires 26 and 27 to the battery, and as soon as the heat generated causes 
the level of the water to rise in the glass water gage 10, open the valve 
in the pipe discharging oxygen into tube 23, and then by pulling down 
the platinum wires to touch the contents of the crucible, the coal will 
be kindled. At the same time the reading of the glass scale opposite 
the gage glass 10 must be observed and recorded. Progress of the com- 
bustion can be observed through the glasses 33, 34, and 36, arranged 
vertically over each other for this purpose. As soon as the combustion 
is complete observe the time and the reading of the scale opposite the 
glass water gage 10. The difference between this last reading and the 
one taken at the beginning of the test is called the " actual " scale read- 
ing. 

The Correction for Radiation is made by observing the reading of the 
scale of the water gage after the oxygen has been shut off, for a length of 
time equal to that required for the combustion. The difference between 
this reading and the " actual " reading is to be added to the " actual " 
reading to obtain the corrected reading. 

By weighing the asbestos cup after the test is finished and subtracting 
from this weight that obtained previously for its weight empty, the 
weight of ash is determined. 

In order that Carpenter's calorimeter may give determinations of 
heat values that are at all accurate, all the air must be removed from 
the water used, as the presence of air 1 will affect the relative level of 
the water in the gage glass for a given rise in temperature. The oxygen 
must also be supplied at a constant pressure, maintaining the pressure 
indicated by the manometer gage at the value for which the calorimeter 
was calibrated. Most calibration curves are made for a pressure of 
about 10 inches of water. The apparatus can be made to give good 
comparative results when operated carefully and " according to direc- 
tions," but the general experience has been that calorimeters of this 

1 About two inches of kerosene oil are usually put into the glass water gage to prevent 
air from coming in contact with the water. 



222 



POWER PLANT TESTING 



type give values that are from one to two per cent too low compared 
with results with a bomb calorimeter due to incomplete combustion. 
In general, the statement is often made that coal calorimeters intended 
for combustion at constant pressure will usually give nothing more than 
" faint approximations " to correct results. 

When making calorific determinations of coal the distinction must 
be carefully made between results obtained per unit weight of combustible 
or per unit weight of coal (including moisture and ash). 

Junkers' Calorimeter for Liquids and Gases. An apparatus for de- 
termining the calorific value of gases is shown in Fig. 267 and Fig. 268. 

The gas flowing in a pipe at the 
left (Fig. 267) passes through 
the meter A, then through the 
regulator B, and is burned in a 
type of Bunsen burner C in the 
lower part of the calorimeter. 
This instrument consists of a 
cylindrical copper vessel 
through which water is con- 
stantly circulating. The gases 
from the Bunsen flame in the 
calorimeter pass up through the 
hollow central portion of the 
instrument and near the top 
are deflected downward through 

Fig. 267,-Junkers' Calorimeter with Auxiliary a S roU P ° f Sma11 tubeS ranged 
Apparatus. m an annular ring between the 

outside and inside walls of the 
calorimeter. 1 Around these tubes water is kept circulating continuously 
to absorb the heat generated by burning the gas tested. After leaving 
these tubes the products of combustion discharge first into a chamber 31 
(Fig. 268) and then into the air through the flue D. In order to keep 
the flow of water as regular as possible it is brought from the supply 
pipe G into a small reservoir in which the water is kept at a constant 
level (constant head) by means of an overflow pipe H. The water 
supplied to the calorimeter passes down through the pipe 6, through a 
valve at I, and discharges at K, running into a vessel in which it is 
weighed. A graduated tube Q (Fig. 267) is provided to collect the 
1 A modification of Junkers' calorimeter is made by the American Meter Company of 
New York and Philadelphia. In principle it is exactly the same as the one described, 
but is much improved in mechanical construction, the greatest advantage being that the 
nest of small tubes can be readily removed for repairs. In the original design removal for 
repairs is difficult if not almost impossible. The "American" type is used exclusively 
by the U. S. Bureau of Standards, which is a sufficient guarantee of reliability. 




CALORIFIC VALUE OF FUELS 



223 



moisture from the steam that is condensed. The condensed steam col- 
lects in the combustion chamber 31 and escapes through the tube 35. 
A thermometer N, in a cup near the valve I, indicates the temperature 
of the water entering the calorimeter, and one at M shows the temper- 
ature of the water leaving. The temperature of the products of com- 
bustion (burned gases) is indicated by the thermometer O in the gas 
flue. The calorimeter is provided with an air jacket and is covered with 
sheets of copper, nickel plated and highly- 
polished so that the radiation loss is consid- 
ered negligible. If, then, the flow of water 
and the rate of burning the gas are regulated 
so that the temperature of the products of 
combustion as indicated by the thermometer 
at O is the same as the temperature of the 
air surrounding the calorimeter, practically 
all the heat generated by the burning gas is 
absorbed by the water. The rise in temper- 
ature of the water is observed by reading the 
thermometers at N and M. 

Now if the temperatures of the water at 
the inlet and the discharge have been ob- 
served and the weight of the water flowing 
has been determined while, for example, a 
cubic foot of gas has been burned, then the 
difference in temperature in degrees Fahren- 
heit times the weight of water in pounds 
gives the heat value in British thermal units 
per cubic foot of gas. This is called the higher 
heat value of the gas. 

Results of calorific determinations of a gas 
should be stated in a report as calculated as 
heat units per cubic foot of gas for the stand- 
ard conditions of pressure and temperature. 
The American Society of Mechanical Engi- 
neers has favored the adoption 1 of 30 inches of mercury pressure (14.7 
lbs. per sq. in.) and 62 degrees Fahrenheit, while chemists and European 
engineers use as standard 29.92 inches (760 mm.) of mercury pressure 
and 32 degrees Fahrenheit (0 degrees Centigrade). This conversion can 
be readily made because the volume of the gas is directly proportional 
to the temperature and inversely to the pressure. 

For some calculations relating to the efficiency of heat engines it is 
desirable to know the number of heat units representing the calorific 
1 Journal A.S.M.E., Nov., 1912, pages 1795-1801. 




Fig. 268. — Section of Junkers' 
Calorimeter. 



224 POWER PLANT TESTING 

value of the gas when the steam formed in. the combustion is not con- 
densed but is carried off with the products of combustion as is the case 
in practice. To determine this value, sometimes called the "lower" 
heat value of the gas, the latent heat at atmospheric pressure of the 
amount of condensed steam collected in the Junkers calorimeter must 
be subtracted from the value obtained by multiplying together the rise 
in temperature and the weight of water used. This correction is usually 
about five to ten per cent, having usually the smaller value for producer 
gases with high percentages of CO. 

When thermal efficiencies of gas. engines are calculated, it should al- 
ways be clearly stated whether the " higher " or the " lower " heat 
value of the gas has been used. In all the codes of the American Society 
of Mechanical Engineers the " higher " heat value has the preference, 
but this is not by any means the generally accepted practice. 

This apparatus, although it operates by a constant pressure method, 
gives very satisfactory determinations. Radiation loss is small and is 
neglected. Since tests with this apparatus are started when all parts 
are already heated normally, no water equivalent is to be taken into 
account. If the temperature of the discharge gases is not the same as 
that of the air supplied the results will be in error but the amount of 
this correction (see page 252, footnote) and the method of computing 
it is uncertain. For this reason the temperature of the discharge gases 
should be regulated most carefully and not more than two or thres 
degrees Fahrenheit difference should be permitted between the tem- 
perature of these gases and that of the air supplied. Often it is neces- 
sary to open the windows of laboratory rooms to secure the proper 
temperatures. Temperatures of the water should be practically con- 
stant before a test is started. 

As the Junkers calorimeter is ordinarily operated it does not determine 
accurately the "higher" heating value even if all the precautions stated 
have been observed. It is because an excess of moisture above that 
which came in with the air goes off in the discharged gases. The only 
way to eliminate this error is to supply gas and air that are saturated with 
moisture. The calorimeter will then give the true " higher " heating 
value, because all the moisture resulting from the combustion of hydro- 
gen will be condensed, and will give up its latent heat. When a wet-gas 
meter is used it may be assumed that the gas is saturated as it comes to 
the apparatus. The obvious way to eliminate this error is to supply air 
which is also saturated. A convenient design is to connect the closed 
top of a cylindrical vessel about two feet high and five inches in diameter 
by a one-inch rubber tube to the bottom of the calorimeter, which, ex- 
cept for the opening for this tube, has been made air-tight. The cylinder 
is provided with a water-waste cock at the bottom. Several trays 



CALORIFIC VALUE OF FUELS 225 

covered with coke are placed inside the cylinder which is perforated 
with a number of half-inch holes around the perimeter near the bottom 
for the admission of air. A water-jet discharges from the top of the 
cylinder and the water trickles down over the coke as the air enters 
at the bottom and passes up to the air-pipe leading to the calorimeter. 
By this method air is thoroughly saturated and not only more accurate 
but also much more consistent results for the " higher " heat values 
are obtained. Obviously this humidity correction has no effect at least 
in the theory of combustion on the " lower " heat values, as they are 
calculated for the condition when all the water vapor due to combustion 
leaves in the discharged gases. This is one reason why many engineers 
prefer to base calculations of thermal efficiency on the " lower " heat 
values. 

The error due to humidity can, however, be calculated approximately 
and the results correspondingly corrected. Moisture carried in the air can 
be determined by a wet- and dry-bulb thermometer (see page 368) and 
then assuming the discharged gases and the gas burned are saturated, 
the excess of condensation carried away in the discharged gases are readily 
calculated since their weight can be determined by a laborious calcu- 
lation involving the computation of the weight of air supplied which 
must be obtained from the analysis of the products of combustion 
(discharged gases). 

For making determinations of the calorific value of suction producer 
gas where the working gas pressure is less than atmospheric, a good 
method is to collect a sample with an aspirator and collecting bottle as 
explained for sampling flue gas (see page 236). 

Producer gas and other gases of low heating value can be mixed with 
a little air and burned in a simple metal tube, covered over at the end 
with a piece of fine gauze to prevent firing back into the mixing chamber. 
The mixture formed should preferably be non-explosive. 

The author has made continuous recording gas calorimeters using a 
simple pipe burner and positive pressure blowers (similar in design to 
those on page 366). One blower for measuring the gas is of about one- 
sixth the capacity of the larger one for measuring the air. Both blowers 
being driven by a single electric motor will always deliver gas and air 
in a constant ratio, provided pressure and temperatures of gas and 
air are maintained at about the values at which the instrument was 
calibrated. Calorific value of the gas is then proportional to the 
difference in temperature between the air and gas entering and the tem- 
perature of the discharged gases. A differential recording thermometer 
with the chart graduated in heat units per cubic foot of gas as determined 
by comparison with a Junkers calorimeter gives a continuous record of 
heat values of the gas. An apparatus of this kind is very useful in a. 



226 



POWER PLANT TESTING 



producer gas plant in showing the quality of gas produced and the rel- 
ative care observed in the operation of the producers. 

Exercise. Calorific Value of Gas. One cubic foot of coal gas at an 
absolute pressure of 28.9 inches of mercury and at 70 degrees Fahren- 
heit when burned in a Junkers calorimeter raised the temperature of 
8.36 lbs. of water from 57.7 to 121.4 degrees Fahrenheit. Weight of 
condensation (water) collected due to combustion was .056 lb. Abso- 
lute atmospheric pressure 14.2 lbs. per sq. in. and corresponding latent 
heat of steam from tables = 971.5 B.t.u. per pound. 

" Higher " Heat Value at " Room " Conditions, B.t.u. per cu. ft. = 
(121.4 - 57.7) X 8.36 = 532.5. 

" Lower " Heat Value at " Room " Conditions, B.t.u. per cu. ft. = 
532.5 - (971.5 X .056) = 478.2. 

Volume of Same Gas at Standard Conditions (30 in. mercury press, 
and 62 degrees Fahrenheit) = 

1X28.9X522 An . n ,, 
30X530 =°- 949c "- ft - 

" Higher " Heat Value at Standard Conditions, B.t.u., per cu. ft. = 
532.5 



.949 



562. 



Lower 



Heat Value at Standard Conditions, B.t.u. per cu. ft. = 
478.2 _.. 

w = 504 - 

Fig. 269 shows a balance and lamp attachments for a Junkers calorim- 
eter set up for determining the heat value of liquid fuels like gasoline, 

kerosene, crude oil, etc. The heat gen- 
erated is measured in the same way as 
when gas is burned and the weight of 
oil used is determined by weighing on 
the balance to which the lamp L is at- 
tached. This lamp is provided with a 
" regenerative " burner B with a long 
stem as shown. A small hand pump 
P is arranged for attachment to the 
valve V to put the oil in the bowl of 
the lamp under a pressure of about ten 
pounds per square inch. This air pres- 
sure forces the oil up the stem and 
through a coil of metal tubing which 
lies above the flame and is heated by it and gasified. The gaseous fuel 
escapes as a jet through a minute orifice where it should burn with a 




Fig. 269. — Balance and Lamp for 
Burning Oils in Junkers Calori- 
meter. 



CALORIFIC VALUE OF FUELS 227 

blue flame indicating perfect combustion. When using oils heavier than 
gasoline the regenerator coil must be heated by burning alcohol in the 
cup shown in the figure just below the burner B. When combustion is 
not complete as is always the case when the flame is started soot ac- 
cumulates on the coil and is likely to choke the orifice of the burner. 
A piece of fine piano wire should always be at hand for cleaning the 
orifice. 

Calorific Values from Chemical Analysis. Dulong stated a long time 
ago that the heat generated by burning any fuel was equal to the sum 
of the " possible heats " generated by its component elements, less that 
portion of the hydrogen which combined with the oxygen in the fuel to 
form water. When hydrogen and oxygen exist together in a compound 
in the proper proportions to form water, the combination of these ele- 
ments has no effect on the calorific value of the compound. Now the 
calorific value of a pound of carbon is 14,600 B.t.u. and of a pound of 
hydrogen is 62,000 B.t.u., so that by Dulong's formula, the calorific 
value of a pound of fuel x would be stated, using these values, as 

x = 14,600 C + 62,000 ( H — -^ J + 4,000 S, . . . (69) 

where C, H, O and S are respectively the weights of the carbon, hydro- 
gen, oxygen and sulphur in a pound of fuel. 

A similar formula known as that of the Verein deutscher Ingenieure 
expressed in units and terms used in Dulong's, but corrected for w per 
cent of moisture is given as follows: 

x = 14,400 C + 62,000 (H — -^-J + 4,500 S — 1,100 w. . (70) 

Formulas given above are all for the " higher " heat values corre- 
sponding to those obtained with a bomb calorimeter. The last formula 
(70) expressed for " lower " heat value is: 

x = 14,400 C + 52,000 (H — -g J — 1,100 w. . . . (71) 

As the result of testing forty-four different kinds of coal with his 
bomb- calorimeter Mahler developed the following formula, using the 
same symbols used in Dulong's, 

x = 200.5 C + 675 H - 5,400. ..... (72) 

Using this latter formula Lord and Haas 1 computed the calorific values 
for a series of 40 Pennsylvania and Ohio coals' which they had analyzed 
and found that the maximum differences between the calculated results 
and the determinations with a bomb calorimeter were from 2.0 to — 1.8 

1 Trans. American Inst, of Mining Engineers, Feb., 1897. 



228 



POWER PLANT TESTING 





\ 


X 




V. 


^\ 


^ 


t 



10 15 20 25 30 35 
Percent Volatile Matter "as Rec'd" 

Fig. 270. — Curve for Determin- 
ing Calorific Value of Coal. 



per cent. With fuels like coke, charcoal, and anthracite coal, in which 
the content of volatile matter is small, the calorific values calculated 
from an accurate analysis are usually in 
very close agreement with accurate calori- 
meter tests, but with coals having more 
than 20 per cent of volatile matter there is 
likely to be considerable error. 

A formula which is as accurate as any of 
those given above is based on the results of 
the proximate analysis. In this formula, 
known as Goutal's, 1 

c = per cent fixed carbon in coal " as re- 
ceived." 

v = per cent volatile matter in coal " as 
received." 

a = constant from the curve in Fig. 270, 
then, 
x = 147.6 c + w. . (73) 

Proximate Analysis of Coal. For all tests in which an analysis of the 
coal or its calorific value is to be determined, it is very necessary that 
the sample to be tested be selected with the greatest care. The method 
generally adopted for obtaining a fair sample is known as " quartering," 
as explained in the Rules for Conducting Boiler Tests adopted by the 
American Society of Mechanical Engineers. (See page 231.) The 
utmost care must be taken that the amount of moisture in the sample 
received for analysis is the same as that in the original condition, or 
more specifically in a boiler test, at the time when the coal used in the 
test was weighed. For this reason samples of coal should be trans- 
ported and stored in air-tight preserving jars or similar vessels. It is 
not unusual, moreover, to find that coal containing 10 per cent of mois- 
ture will lose as much as 2 or 3 per cent of its moisture in the process of 
careless sampling, crushing, resampling, etc., while if it is allowable to 
remain exposed to atmospheric conditions for a considerable time in a 
warm room as much more may be lost by evaporation. Crushing, 
sampling, and weighing should always be done as rapidly as possible. 

Only during recent years has the proper importance of correct sampling 
of coal for analysis been understood. Particularly in run-of-mine coal, 
that is, coal as mined without crushing or screening, the careful selection 
of coal for the sample as regards size is also very important. If the sam- 
pling has not been done so as to get coal that is representative, certainly 
the analysis can be of no value. Proportionate amounts should be 

1 Wisconsin Engineer, Dec, 1911. 



CALORIFIC VALUE OF FUELS 229 

taken of both large and small sizes as well as of the fine dust. In the 
best engineering practice to-day at least 200 pounds of coal is collected 
for the process of sampling for the analysis. This amount of coal is 
to be broken up on a clean floor by any convenient means to a size of 
about | inch diameter, then thoroughly mixed and spread out on a flat 
circular pile. This pile is then " quartered," and opposite quarters are 
discarded. The remainder is now further broken up to about | inch 
diameter and the mixing, quartering and discarding is continued until 
from five to ten pounds remains. This is to be put into a glass jar or a tin 
can that can be made air-tight. The sealing should be carefully done, 
to prevent any deterioration of the sample in transportation to the 
laboratory where the analysis is to be made. 

In the laboratory the coal should be emptied from the jar or can and 
crushed to a fineness of about a 20-mesh sieve (20 meshes to the inch). 
The crushed coal is thoroughly mixed and a small portion, about 2 or 3 
ounces, is put into an air-tight bottle and is to be used for the analysis. 
The rest is put back into the jar or can and sealed. It is to be retained 
for possible use in check tests. 

Proximate analysis of coal consists in determining the moisture, 
volatile matter, fixed carbon, ash and sulphur. Methods for these 
determinations are more or less empirical and vary slightly, so that 
in a report the authorship of the methods used should be stated. The 
methods most generally accepted by progressive engineers are those 
defined by the American Chemical Society, 1 and are in common use both 
in this country and in England. 2 

Moisture and ash determinations are most important because they are 
non-combustible are detrimental constituents, the moisture requiring the 
wasting of heat for its evaporation into steam and the ash when present 
in large amounts is often likely to form clinker in poorly designed or 
badly operated furnaces and is also expensive to dispose of. Sulphur 
determinations are important only when the furnaces are not suitable for 
the combustion of coal containing one or two per cent of sulphur. Fur- 
naces are readily designed for burning coals having from four to five per 
cent of sulphur without clinkering the ash. 

Methods of the American Chemical Society are as follows : — 

1. Moisture. Weigh in a covered crucible about four grams (about 
| oz.) of the coal passing through a 20-mesh sieve that was prepared for 
analysis as described above. This should be done as quickly as possible 
to avoid loss of moisture to the air. Remove the cover and heat in an 
oven for an hour at a temperature of from 220 to 230 degrees Fahrenheit. 
At the end of the hour replace the cover on the crucible, remove it from 

1 Journal of American Chemical Society, vol. 21 (1899). 

2 The Testing of Motive Power Engines, by R. Royds (London, 1911), page 293. 



230 [POWER PLANT TESTING 

the oven and place it in a desiccator to cool. 1 When the crucible and 
the coal it contains are at nearly the same temperature they should 
be weighed. Again remove the cover and heat as before in the oven 
for a half hour longer. If the weight has remained constant no more 
heating is necessary and the difference between the first and last weigh- 
ings is the moisture in the coal. 

2. Volatile Matter. Weigh about one gram Q$ oz.) of the " 20- 
mesh " crushed coal prepared for analysis in a platinum crucible weigh- 
ing from 20 to 30 grams (f to 1 oz.) 2 having a closely fitting cover. Support 
the covered crucible on a chemist's triangle of nichrome steel or of 
platinum which should be about 3 to 3| inches above the top of a good 
Bunsen burner. 

Heat the covered crucible for seven minutes in the full flame of the 
burner which should be at least eight inches high when unobstructed. 
Cool the crucible in a desiccator and then weigh carefully. The loss is 
the sum of the volatile matter plus the moisture. The room in which 
the test for volatile matter is made should be free from drafts which might 
cause a variation in the intensity of the flame. 3 

3. Fixed Carbon and Ash. The crucible without the cover and the 
residue from the preceding test are now intensely heated with a Bunsen 
flame or with an air-blast lamp until all the carbon has been burned, and 
the weight of crucible and contents becomes constant. The use of the air- 
blast lamp in place of the Bunsen burner for this last determination will 
very much reduce the time required. The contents of the crucible may 
be stirred slightly with a platinum wire to break up the ash which should 

1 While the sample is cooling there is the possibility that it may absorb moisture 
from the air unless it is placed in a desiccator until cool. It is difficult to get accurately 
the weight of hot bodies on account of the air currents produced. 

2 The capacity of the crucible should be about three times the volume of the coal 
to allow for its expansion in coking. 

3 It is not at all unusual for persons making tests on the same sample of coal to dis- 
agree as to the volatile content. This is because not all chemists and engineers will 
use the same type of burner, and if they are in different places they may have gas of 
widely different heat value. To overcome these difficulties the author has made electric 
furnaces consisting of a single resistance coil of nichrome wire calibrated for an im- 
pressed wattage to give a temperature of from 850 to 900 degrees Fahrenheit in a plati- 
num crucible placed in its core. In five minutes after the electric current is applied 
to the coil a constant and maximum temperature is reached and the covered platinum 
crucible is then inserted to be heated for seven minutes. Weighings are made as with 
the regular method. Results show remarkably close agreement, and are independent 
of variable gas supplies. 

Porcelain crucibles should never be substituted for platinum crucibles for accurate 
work as the porcelain requires a longer time to attain a constant temperature and 
therefore the duration of the application of the maximum temperature may not be the 
same as with one of platinum. 



CALORIFIC VALUE OF FUELS 231 

become a powdery mass when combustion is complete. Combustion is 
assisted by inclining the crucible on the triangle during this test so as 
to admit air more freely for oxidation. After cooling in a desiccator 
make a final weighing. The difference between this weight and 
that of the crucible without cover when empty is the ash. Weight 
of fixed carbon is obtained by subtracting the sum of the weights of 
moisture, volatile matter and ash from the original weight of the sample 
of coal tested. 

Weighings should be made with chemical scales sensitive to TJJ \ o of the 
amount weighed. Two determinations of the complete proximate 
analysis should be made of each sample and the results should check 
within half of one per cent of the weight of the coal. 

In a report record with the regular data whether in the volatile test 
the coal coked into a single spongy mass or whether it remained granular. 

A. S. M. E. Methods. Methods proposed for poximate analysis of 
coal by the Power Test Committee of the American Society of Me- 
chanical Engineers vary somewhat from the above. The following 
important items should be cited: 

1. In tests where firing is done by hand select a representative shovel- 
ful from each barrow-load as it is drawn from the pile and store the 
samples in a cool place in a tightly covered metal receptacle. 

When all the coal has thus been sampled, break up the lumps, 
thoroughly mix the whole quantity, and finally reduce it by the process 
of repeated crushing, quartering and discarding opposite quarters to a 
sample weighing about 5 pounds, the largest pieces being about the size 
of a pea. From this sample two one-quart air-tight glass fruit jars, or 
other air-tight vessels, are to be promptly filled and preserved for sub- 
sequent determinations of moisture, calorific value and chemical com- 
position. These operations should be conducted where the air is cool 
and free from drafts. 

When in the process of quartering and discarding the sample lot of coal 
has been reduced to about 100 pounds, a portion weighing say from 15 to 
20 pounds should be withdrawn for the purpose of immediate moisture 
determination. This is placed in a shallow iron pan and dried on the 
hot iron boiler flue for at least 12 hours, being weighed before and after 
drying on scales reading to quarter ounces. 

The moisture thus determined is approximately reliable for anthra- 
cite and semi-bituminous coals, but not for coals containing much 
inherent moisture. For such coals, and for all absolutely reliable 
determinations, the method to be pursued is as follows: 

Take one of the samples contained in the glass jars and subject it to 
a thorough air-drying, by spreading it in a thin layer and exposing it for 
several hours to the atmosphere of a warm room, weighing it before and 



232 POWER PLANT TESTING 

after, thereby determining the quantity of surface moisture it contains. 
Then crush the whole of it by running it through an ordinary coffee 
mill or other suitable crusher adjusted so as to produce somewhat coarse 
grains (less than T V inch), thoroughly mix the crushed sample, select 
from it a portion of from 10 to 50 grams, 1 weigh it in a balance which 
will easily show a variation as small as 1 part in 1000, and dry it for one 
hour in an air or sand bath at a temperature between 240 and 280 de- 
grees Fahrenheit. Weigh it and record the loss, then heat and weigh 
again until the minimum weight has been reached. The difference 
between the original and the minimum weight is the moisture in the air- 
dried coal. The sum of the moisture thus found and that of the surface 
moisture is the total moisture. 

To determine volatile matter place one gram of air-dried powdered 
coal in the crucible and cover it with a loose platinum plate. Heat 
3^ minutes in the flame 2 of the Bunsen burner, and continue the heat- 
ing for 3| minutes longer in the flame of the blast lamp. Cool down, 3 ' 
remove the cover, and weigh the residue. The loss in weight repre- 
sents the combined volatile matter and moisture. Subtracting the 
moisture, the weight of volatile matter alone is determined. 

To ascertain the ash expose the residue in the crucible to the blast 
lamp until it is completely burned, using a stream of oxygen if desired 
to hasten the process. The residue left is the ash. 

The difference between the residue left after the expulsion of the vola- 
tile matter and the ash is the fixed carbon. 

To determine sulphur by Eschka's method, which is the one com- 
monly used, heat 1 gram of coal mixed with 1 gram of magnesium oxide 
and ^ gram of sodium carbonate for 1 hour, using an alcohol lamp. After 
cooling mix with 1 gram of ammonium nitrate and heat the mixture 10 
minutes; then dissolve in 200 cc. of water, heat and reduce by evapora- 
tion to 150 cc, acidify with hydrochloric acid and filter. Add barium 
chloride to the filtrate and determine the sulphur by calculation from 
the quantity and composition of the barium thereby precipitated. 

The carbon and hydrogen are obtained by the use of the combustion 
apparatus. One-half gram of the pulverized air-dried coal is placed in 
a porcelain "boat," which is introduced between the copper roll of oxi- 
dized copper gauze and the copper oxide within the glass combustion 
tube. After the coal and the entire contents within have been thor- 
oughly dried out by a sufficient preliminary heating, aided by a current 
of dry air, the furnace is set to work and the coal burned by first passing 

1 About i ounce to 2 ounces. 

2 Height of flame is not specified. It could be stated that it should be in the hottest 
part of flame as in some coal specifications. 

3 Cool in a desiccator. 



CALORIFIC VALUE OF FUELS 233 

air through the tube and finally oxygen. The products of combustion are 
to be passed through potash bulbs and a chloride of calcium tube. The 
carbon dioxide produced by the combustion of the carbon is absorbed 
by the potash, and the water formed by the combustion of hydrogen, 
together with that due to the moisture in the air-dried coal, is taken 
up by the chloride of calcium. The quantity of carbon is determined 
by weighing the bulbs before and after, thereby obtaining the weight 
of the carbon dioxide produced, and then calculating the weight of 
carbon from the known composition of the dioxide. Likewise, the 
quantity of hydrogen is determined by weighing the calcium tube 
before and after, which, after deducting the moisture in the air-dried 
coal, gives the amount of water produced, and, dividing by 9, the amount 
of hydrogen. 

The ultimate analysis of coal for sulphur, pure carbon and hydrogen, 
as will be seen from the above description, requires the use of so much 
chemical apparatus, and at best it is so complicated, that it is not likely to 
be done except in a fully equipped chemical laboratory. It should not be 
undertaken by one who is not entirely familiar with all the details of the work. 

Hydrogen from Proximate Analysis. Professor L. S. Marks 1 has de- 
veloped an empirical formula for the determination of the hydrogen in 
coal from the proximate analysis. In this formula V is the per cent by 
weight of volatile matter in the combustible part; that is, coal less the 
sum of moisture and ash, and H is similarly the per cent by weight of 
hydrogen in combustible, then, 

7-35 



H = V(^ 



+ 10 



.013 



Purchasing Coal by Calorific Value (" B. t. u's ") and Analysis. 

Every year there are more power plants purchasing their coal on the 
basis of analysis and calorific value. It may be generally assumed that 
shipments of coal coming from the same mine at different times will 
not vary a great deal in the composition of combustible. Moisture and 
ash may however vary considerably and every large shipment, pref- 
erably every car-load should be tested at least for moisture and ash 
content as a check to determine whether the specifications are being 
fulfilled. At frequent intervals particularly when ash or moisture 
determinations indicate a doubtful quality, samples should be sent to 
some laboratory for a complete analysis. For only the moisture and ash 
determinations no special equipment is needed. If moderately large 
weights are used, a fairly accurate " counter " or even a good plat- 
form scales may be used for weighing; and aside from this only a few 
sheet metal or tin pans, one or two thermometers, and several Bunsen 

1 Power, Dec, 1908. 



234 POWER PLANT TESTING 

burners and porcelain crucibles are absolutely required. 1 Besides the 
scales for weighing the equipment needed can be purchased for ten 
dollars. For a drying box almost any kind of a discarded galvanized 
iron or tin vessel can be used. There should be a small hole in the top 
for the insertion of a thermometer. 

To burn coal to ash with Bunsen burners requires the application of 
heat for a great many hours. Instead of providing air pressure for 
a blast lamp some engineers prefer to buy oxygen in tanks 2 and burn 
the coal rapidly in a pure oxygen atmosphere. 

1 For a more complete discussion of the sampling and analysis of coal as well as 
criticisms of sample specifications, see Bulletin No. 5, The Pennsylvania Engineering 
Experiment Station, State College, Pa. (Free distribution.) 

2 Linde Air Products Co., Buffalo, N. Y., with distributing stations in several large 
cities. 



CHAPTER IX 



FLUE GAS ANALYSIS 



Flue Gas Analysis. The analysis of flue gases in connection with 
tests of steam boilers gives a valuable means for determining the relative 
value of different methods of firing and of different types of furnaces. 
Errors in the analysis of flue gases are most often due to the inability to 
secure an average sample of the gases in the different parts of a flue 
or chimney. The composition is likely to vary considerably even 
during short intervals, and it is therefore desirable to adopt some method 
of sampling which will permit collecting the sample slowly and continu- 
ously for a considerable period. 

A very simple and convenient sampling apparatus is shown in Fig. 275. 

The sample of gas 1 is taken from the flue or chimney through the 
pipe P shown at the top of the figure. This pipe extends well into the 
flue and has usually a long slot cut into its side so 
that presumably a better sample of gas can be taken 
than if it were taken at the end of the pipe. The pipe 
outside the flue is connected by means of a short rub- 
ber tube to the sampling bottle. A valve V should be 
put as near as possible to the end of such pipes, so 
that they can be closed up when the sampling bottle 
is removed for analysis. If the pipe cannot be closed, 
the suction in the flue will draw air into the pipe and 
fill it so that when again connecting up the sampling 
bottle all this air must be removed before a true sam- 
ple can be taken. The sampling bottle is preferably 
one with a wide neck, closed with a rubber stopper 
through which two glass tubes pass into the bottle, 
one reaching nearly to the bottom and the other en- 
tering only a little below the stopper. Tube B can be connected to an 
aspirator or ejector, or any similar device producing a suction, and there 
will be a steady flow of gas through the bottle. If still another short 
tube like B is put into the stopper it can be used for the attachment of 
gas analysis apparatus, making a very satisfactory arrangement, and it 
is then unnecessary to disconnect the sampling bottle from the pipe. 

Small aspirators or ejectors (Fig. 276) operating on the principle of 

1 For further discussion of sampling of the gas see " Boiler Code — Location of In- 
struments," page 272. 

235 




Fig. 275.— Gas Sam- 
pling Bottle. 



236 



POWER PLANT TESTING 




an injector with a small stream of water which entrains the gases is 
very convenient for collecting samples continuously. A slightly different 
design made of pipe fittings is shown in Fig. 277. 
a | ter Water enters through a vertical nozzle N and in 
discharging as a jet at high velocity entrains air 
or gas drawn in through the side opening and 
the mixture of atomized water and air is dis- 
charged with considerable velocity through the 
forcing tube F at the bottom. 

If an aspirator is not available, the sampling 
bottle and the tube B may be filled with 
mercury. Then by gradually siphoning the mer- 
cury from the bottle the flue gases will be 
drawn in. 

By adjusting the valve V the rate of flow of 
the gases into the bottle can be regulated. Mer- 
cury is too heavy to use in a very large sam- 
pling bottle so that water is often used instead, 
with the disadvantage, however, that the water 
will probably absorb some of the constituents 
of the gas. On this account very little water 
should be left in the bottle with the sample of 
gas. If the water is saturated with gases, as it will be from long use, 
this precaution is not so essential. Sampling and collecting bottles 
should have rubber rather then cork stoppers, because cork is too porous. 1 

The sampling bottle and the tubes must be com- 
pletely filled with the liquid before beginning to 
take the sample by the method of displacing water, 
because any air left in them will remain in the 
bottle and will be mixed with the sample of the gas. 
If the end of the stopper going into the bottle 
is made slightly conical it will be easier to avoid 
entrapping bubbles of air at the top of the bottle 
when inserting the stopper. 

This type of sampling bottle when filled with 
liquid can be used also very conveniently by re- 
versing the connections of its tubes; that is, by 
attaching the long tube to the pipe entering the 
flue, and then turning the bottle upside down. The 
liquid will then run out through the shorter tube 
and the gas will be drawn in to fill the bottle. 



Discharge 
Fig. 276. — Water-jet As- 
pirator or Ejector. 



Bushing 




Fig. 277. 
made of Pipe Fit- 
tings. 



1 A good way to cut holes in rubber stoppers for tubes is with the ordinary drills 
used for metal work, using a drill considerably larger than the hole required. 



FLUE GAS ANALYSIS 



237 



A portion of the gas can be removed from the sampling bottle into the 
measuring burette or tube required for making the analysis of the flue gas 
by connecting the short tube of the sampling bottle to the burette or to 
some other part of the gas analysis apparatus as may be required. If 
now the rubber tube connected to the longer tube of the sampling bottle 
when disconnected is put into a pail well filled with water, then as the gas 
is withdrawn from the bottle, water will be drawn from the pail to dis- 
place it. One of the advantages of this sampling apparatus is that it can 
be easily made from the materials obtainable in almost any town or 
village. A two-quart preserving jar with a rubber stopper to fit and tubes 
of glass, brass or iron can be used to make up a very good apparatus. 

Fig. 278 shows a sampling device used extensively in England. It 
consists of an iron tube T of f -inch-iron pipe open only at the end in the 
flue. The end is located carefully how- 
ever in English practice so that it lies 
well into the current of the gases. The 
pipe T is connected to a vessel M about 
two feet in diameter. The bottom is 
connected to another vessel of about the 
same size which is open at the top to the 
atmosphere. Samples for analysis are 
taken from the small bottle A. Vessels 
M and N are provided to prevent stag- 
nation of the gases in the pipes. Rubber 
tubing is used in only very short lengths 
because it is said to be more or less 
porous to C0 2 . When the test is started 
the bottle A is full of mercury, cock C is 
closed, and D is open just enough to permit a slow flow of mercury into 
B. When a new test is to be started the mercury in B is poured into 
C and A is filled and slowly emptied as before. 

Since there is nearly always a great variation in the composition of 
the gases in the various parts of a flue or chimney it is not very likely 
that a tube open at the end and having a long slit like the one described 
in the preceding paragraphs will give a " fair " sample. Obviously 
most of the gas will enter the slot in that portion of its length nearest 
the collecting apparatus. Another device often used for a sampling 
tube consists of a horizontal pipe into which a number of branch tubes 
are fitted. These branch tubes are arranged so that the openings at 
their ends will take samples from the different parts of the flue or chim- 
ney in which they are placed. Sometimes these branch pipes are also 
slotted or are perforated with small holes drilled into their walls. 

Fig. 279 shows an arrangement of sampling tubes for collecting flue 




V/*« 



Fig. 278. — English Gas Sampling 
Apparatus. 



238 POWER PLANT TESTING 

gas recommended by the American Society of Mechanical Engineers 
in the code of 1899. It consists of a series of standard one-fourth inch 
pipes, all open and otherwise alike at the ends and of equal lengths. 
Each pipe is to be placed with one end in a shallow air-tight box or 
receiver made of sheet iron. It is convenient usually to make the depth 
of this sheet-iron box about the same as that of a course of bricks. These 
tubes should be arranged so that the open ends will be at points well 
distributed over the area of the flue which in the figure is marked A. 
The other ends, which are also open, are to be enclosed in the receiver 
B. The receiver is connected by four tubes C, C with a mixing box D. 
The flue gases drawn from it should be well mixed and should represent 
an average sample from the flue or chimney from which they are taken. 
Tests have shown that two such sampling devices placed in the same 
flue one above the other about a foot apart, will furnish samples of the 
flue gases showing the same composition when analyzed. There are 
several reasons why this apparatus having for a number of years the 
approval of the national societies was scarcely ever used. First, it is 
very expensive costing about $25 for each installation, and second, it 
is difficult to keep air-tight in large sizes. The recent recommendation 
of the Power Test Committee is that a single tube be used having 
perforations " extending the whole length of the part " immersed ", and 
pointing toward the current of gas, the collective area of the perfora- 
tions being less than the area of the pipe." Many American engineers of 
repute prefer a single pipe open only at the end like the one in Fig. 278, 
and observe extreme care in its location to get an average sample. 

A very convenient type of sampling bottle is shown in Fig. 280. It 
consists of a bottle with an opening at the bottom (tubulated), and is 
provided with a stopper at the mouth through which a glass funnel F and 
a tube are passed. The bottle contains water and light oil, and when it 
is filled there will be a layer of about 4 inches of the oil over the water. 
The tube O at the top is to be connected to the sampling tubes in the 
flue and the sample is taken in by opening the valve in this tube and 
also the one at the bottom of the bottle. The water drains off at the 
bottom and is replaced by the sample of gas. The glass funnel is used 
for pouring water into the bottle and in this way expelling the gas 
needed for analysis. The gas is thus made to pass out through the same 
tube through which it is drawn in. 

Another type of sampling apparatus used by many engineers consists 
of two galvanized-iron tanks, each about 2 feet high, and about 5 inches 
in diameter. On the side of each of these tanks and close to the bottom 
a valve is attached by soldering. These two valves are connected by a 
piece of heavy rubber tubing. One of the tanks is closed at the top, and 
a small stopcock or valve is attached to the cover. The other tank is 



FLUE GAS ANALYSIS 



239 



open at the top. The apparatus is used for collecting gas by filling to 
" overflowing " the tank with the closed top with water from the other 
tank by raising the latter so that the level of the water in it is above 
that of the water in the closed tank. By means of rubber tubing the 
stopcock or valve on the closed tank is then connected to the sampling 
tubes in the chimney or flues. Meanwhile the open tank is held at such 
an elevation that the water will not run back into it and create a vacuum 
in the closed tank. After this connection has been made the stopcock 
and valves are to be opened again, so that when the open tank is placed 
below the level of the closed one, the water will flow into the open tank 




Fig. 279. — A.S.M.E. Arrangement of Sam- 
pling Tubes for Flue Gas. 




Fig. 280. — Another Type 
fo Sampling Bottle. 



and fill the other one with gas. This operation should be repeated 
several times before the sample is carried away to be analyzed, so that 
there can be no doubt that none of the air in the sampling tubes en- 
tered the sample to be analyzed. This water can be used over and 
over again, and when it has become saturated with gas it is practically 
as good as mercury for use in collecting the gases. 

When a sample of flue gas is taken from the flue at a considerable 
distance from the furnace it is likely to become mixed with air leaking 
through the brickwork of the boiler setting, and the analysis will not 
show the true relations between the volumes of the so-called flue gases 
and the excess of air. To prevent as much as possible this leakage of 
air the joints in the masonry must be examined and repaired if neces- 
sary and the sample must be taken as near as possible to the fire, bear- 



240 



POWER PLANT TESTING 



ing in mind, however, that they must be drawn very slowly from the 
hot flue in order that they will be cooled down gradually to avoid dis- 
sociation. For hot gases an earthenware collecting vessel may be used 
if a glass bottle is likely to be broken. If dissociation occurs in the 
sample the analysis may show results entirely different from the true 
composition of the gas in the flue. It is also difficult to prevent the 
entrance of air into a flue through the bearings of dampers, and when- 
ever it is possible the sample of flue gas should be obtained between the 
furnace and the damper. At high temperatures sampling tubes of other 
metals than platinum 1 or nickel are not quite satisfactory, since by their 
oxidation they abstract the oxygen from the gases passing through 
them. 

Apparatus for the Analysis of Flue Gases. Samples of flue gases con- 
tain in varying amounts carbon dioxide (carbonic acid), oxygen, carbon 
monoxide, nitrogen, unburned hydrocarbons, and occasionally some 
free hydrogen. For the data which an engineer usually requires it is 
not necessary to determine by direct analysis more than three of these; 
carbon dioxide, C0 2 , oxygen, 2 , and carbon monoxide, CO. 

The determination of CO with the facilities and the portable apparatus 
ordinarily available in engineering laboratories is often somewhat 
doubtful. Some authorities state that there is rarely more than a 
trace of CO to be found in the gases from combustion in the ordinary 
types of furnaces. When more than one per cent of CO is shown by 
the analysis and the CO2 determination is not over 14 per cent, it may 
usually be assumed that a large part of what is taken to be CO is oxygen 
which was not absorbed by the proper reagent. * 

In the following table a set of analyses of flue gases is shown. The 
determinations were made by Scheurer-Kestner with coal from Ron- 
champ. Other analyses of flue gases may be checked by a comparison 
with this table. Thus when the analysis shows about 8.2 per cent 
C0 2 , the sum of the percentages of C0 2 and 2 will probably be between 
19 and 20. 

PERCENTAGE COMPOSITION OF FLUE GAS 



co 2 


o 2 


CO 


N 


Hydrocarbons. 


8.2 


11.3 


.2 


79.8 


.5 


10.8 


9.0 


.2 


79.7 


.3 


12,9 


5.5 


.2 


80.3 


1.1 


13.4 


4.4 


.2 


80.2 


1.8 


14.6 


2.8 


.3 


80.6 


1.7 



1 Porcelain and annealed glass are 
sampling tubes for very hot flues. 



satisfactory materials to use for making 



FLUE GAS ANALYSIS 241 

In the portable apparatus used by engineers for the analysis of flue gases 
a separate pipette or treating tube is provided for each reagent, and the 
chemicals used are of greater strength than the reagents used by some 
chemists. The following reagents give satisfactory results in a portable 
apparatus : 

(1) For absorbing C0 2 a solution of one part of potassic hydrate or 
caustic potash (KOH) dissolved in two parts by weight of water is 
generally used. 

(2) For absorbing O2 either an alkaline solution of pyrogallic acid 1 or 
sticks of phosphorus are employed. 

The alkaline solution of pyrogallic acid is prepared by mixing together 
preferably in the absorption pipette or treating tube, to prevent access of 
air, 5 grams of pyrogallic acid powder and 100 cubic centimeters of 
potassic hydrate (KOH) solution prepared as explained above. 

To make the absorption more rapid some engineers use a solution very 
much stronger in pyrogallic. This is not good practice as stronger 
solutions are likely to evolve CO in the presence of oxygen. 

Phosphorus is more rapid in its action than the pyrogallate, but has 
the disadvantage of being difficult to use as it must be handled under 
water. 

(3) For absorbing carbon monoxide a hydrochloric acid solution of 
cuprous chloride is used. This is prepared by dissolving about 10 
grams of cupric oxide in from 100 to 200 cubic centimeters of concentrated 
hydrochloric acid. This solution must be allowed to remain in a bottle 
tightly closed and well filled with copper wire or gauze, until the cupric 
chloride is reduced to cuprous chloride. In this latter state the liquid 
will be colorless. Exposure to the air produces a brown color, indicating 
the cupric state. 

After a time these reagents must be replaced by new solutions. The 
potassic hydrate solution may be used until each volume has absorbed 
forty volumes of C0 2 . Pyrogallic acid solution deteriorates rapidly and 
each volume should be expected to absorb only one or two volumes of 2 . 
Cuprous chloride will absorb an equal volume of CO. 

Portable devices for the analysis of flue gases are generally known as 
" Orsat " apparatus. Of these there are various types. The one 
devised by Fisher, shown in Fig. 281, has been used extensively. It 
consists of a measuring-tube M surrounded by a water-jacket, and set 
of absorption pipettes, A, B, C, each filled with a reagent. Each of these 
pipettes (Fig. 282) consists of two glass vessels connected by a U-shaped 
glass tube at the bottom. One end of these pipettes is joined by means 
of a short piece of rubber tubing to a glass yoke T, which is designed for 

1 When the temperature is lower than about 55 degrees Fahrenheit this reagent 
does not give satisfactory results. 



242 



POWER PLANT TESTING 



attachment at one end to a tube leading to the sampling-bottle and at 
the other end to the measuring-tube. A water bottle W is connected 
by a flexible rubber tube P to the bottom of the measuring tube. 

Before a sample of gas is taken into the apparatus for analysis certain 
adjustments must be made. In the first place, the reagents in the 
pipettes must all be brought to a standard level at some arbitrary point, 
usually indicated by a scratch on the glass tube just below the short 
rubber tube connecting it to the manifold yoke. This adjustment is 





Fig. 281. — Fisher's "Orsat" Apparatus. 



Fig. 282. — Pipette of Fisher'; 
"Orsat" Apparatus. 



accomplished by opening, one at a time, the valves at the tops of the 
pipette and removing the air (or the gas as the case may be) from it by 
lowering the water level in the measuring tube. The position of the 
water bottle determines, of course, the level of the water in the measuring 
tube. When all the air and gases remaining from a previous test have 
been expelled from the apparatus by filling the measuring tube and 
the tubes comprising the yoke with water, one of the tubes in the sampling 
bottle should be connected to the apparatus at e and by opening the 



FLUE GAS ANALYSIS 243 

valve in the yoke at that end and lowering gradually the level of the 
water in the measuring tube M,a sample is obtained for analysis. This 
sample must be measured by the scale on the measuring tube at atmos- 
pheric pressure 1 to the nearest tenth of a cubic centimeter. 2 After 
the measurement has been made and recorded if the cock in the tube lead- 
ing to the absorption pipette containing the reagent for absorbing C0 2 
is opened and then the water bottle is raised, all of the measured sample 
of gas can be forced over into the pipette. The reagent acts more 
rapidly on the gas if the water bottle is raised and lowered a few times. 
This movement of the water in the measuring tube agitates the gas and 
also the reagent and exposes more of the gas to the direct action of the 
absorbent. To increase the surface over which the reagents can act, 
the pipettes are filled with small glass tubes. When the gas has been in 
the first pipette for about a minute, it should be drawn back into the meas- 
uring tube with the level of the reagent brought back to the mark where it 
was originally, and the cock should be closed. The pressure of the gas is 
again made atmospheric and its volume measured. Now repeat this 
operation until two or three measurements are obtained which are alike, 
showing that all the C0 2 has been absorbed. Then the cock on the tube 
leading to the pipette containing the absorbent for oxygen can be 
opened, the gas forced over, and measured several times until a constant 
volume is observed. Finally the gas is passed into the third pipette 
for absorbing CO, repeating the operation of measuring as with the other 
pipettes. 

The absorption of oxygen will usually require considerably more time 
than for the determinations of the carbonic acid (C0 2 ) and the carbon- 
monoxide (CO), so that it is unnecessary to make a measurement of the 
gas until after the gas has been exposed for about three minutes to the 
reagent. Soft rubber bulbs or bags (see Fig. 282) should be attached 
by means of glass tubes to the corks shown in the pipettes on the farther 
side in Fig. 281 and are provided to protect the reagents from absorbing 
oxygen from the air. Both pyrogallic acid and cuprous chloride will 
absorb oxygen from atmospheric air, so that the access of fresh air must 
be prevented. The rubber bags are useful also for the purpose of pro- 
ducing alternately, with the pressure of the hand, suction and pressure 
for agitating the reagents. 

Allen-Moyer Gas Apparatus. A form of flue gas apparatus particu- 
larly suitable for portable use, and in which renewals of broken parts 
can be cheaply and easily made, is illustrated in Fig. 283. This appa- 

1 The pressure of the gas is " atmospheric" when the water bottle is held so that 
the water in it and that in the measuring tube are at the same level. 

2 The scales of practically all measuring tubes used for gas analysis apparatus are 
graduated in cubic centimeters. 



244 



POWER PLANT TESTING 



ratus, designed by Professor John R. Allen and the author, 1 is also 
particularly suitable for the use of engineers because the pipettes con- 
taining the reagents can be removed from the apparatus very easily 
for changing solutions. They can be emptied, refilled, and replaced in 
a very short time. The absorption pipettes (Fig. 284) are made simply 
of two glass test-tubes, the smaller one inside the larger one. The small 
test-tube is held inverted, and has a very small glass "capillary" tube 
fused into its closed end. The outer tube is closed at the top by a rubber 
stopper through which the capillary portion of the inner tube passes. 
Very small glass tubes are placed in the inner test-tube to increase the 
h 




Fig. 283. — Allen-Moyer Gas Apparatus. Fig. 284. — Absorption Pipette of 

Allen-Moyer Gas Apparatus. 

surface for the action of the reagent. The complete pipette is held in 
place by means of a hard-rubber disk supported on brass screws. The 
level of the reagent in the pipette is established when the air in the inner 
tube is drawn out and the level of the liquid rises to a mark on the glass 
capillary tubes. In the usual forms of the Orsat apparatus the pipettes 
invariably become leaky at the stopper provided for emptying. In the 
Allen-Moyer apparatus there is no opportunity for such leakage. 

When the sample of the gas is passed through the capillary tube into 
the inner test-tube, the reagent is displaced and raises the level in the 
outer test-tube. Similarly when the gas is passed back into the measur- 
ing tube the level falls in the outer tube, rises in the inner one, and is 
1 Made by Bausch & Lomb Co., Rochester, N. Y. 



FLUE GAS ANALYSIS 245 

brought back to the original level at the mark on the capillary tube. 
Otherwise the method of operation is the same as described for Fischer's 
apparatus (Fig. 281). 

In this apparatus the measuring tube M and water bottle W are of 
the conventional type. The yoke is also similar, although usually made 
of hard rubber to avoid breaking it in transportation. It has also spring 
pinchcocks instead of ground-glass cocks. When glass cocks are used by 
inexperienced persons all sorts of difficulties are likely to result, as it 
often happens that they are not pressed into their seats tightly enough 
to prevent the loss of gas or the entrance of air. Sometimes the glass 
cocks will be put into their seats so tightly that it is impossible to move 
them without breaking. These difficulties, although met often enough 
in laboratory work, are still more frequently observed in practice. 

It sometimes happens that, when a, b or c are open, and the pinch- 
cock on the tube between M and W is closed, the reagent in A, B or C 
fails, due not to a leak, as is usually supposed, but to the weight of the 
column of the reagent expanding the gas. 

In case any of the reagent in A or B be drawn over into the measuring 
tube and into the water, the analysis is not spoiled but may be continued 
by flushing out the tubes with water through d or e, or the addition of 
a little hydrochloric acid to the water in W will neutralize the hydrate 
or pyrogallate and the washing may be postponed until convenient. 

To remove pipettes A, B or C when necessary to renew the reagents, 
disconnect the gas bags and the rubber tube which connects the glass 
capillary and rubber capillary tubes, loosen the supporting screw and lift 
the pipette out. The rubber stopper may now be removed and solu- 
tions changed. 

Gases should be cooled well in the sampling bottle before beginning 
the analysis, because such gases change ¥ ^ T of their volume for a varia- 
tion of one degree Fahrenheit, or a change of 1 per cent in volume for 
4.91 degrees. As an example, if the actual percentage of C0 2 is 10, 
and during the time required for analysis the temperature changed 
4.91 degrees Fahrenheit, then there will have been a shrinkage of a vol- 
ume of one per cent due to temperature, and the apparent volume of 
CO2 will be eleven instead of ten. 

Producer Gas Analysis. For the analysis of producer and city 
illuminating gases which are more complex than the flue gases from 
coal furnaces the Hempel apparatus is generally used. Typical parts 
of the apparatus are shown in Figs. 285 and 286. It is slightly more 
difficult to operate and must be handled with greater care than a simpler 
portable apparatus arranged for flue gas analysis. 

. Essential parts of the apparatus are shown in Fig. 285. They are the 
leveling tube L, a measuring burette B, and an absorption pipette P. 



246 



POWER PLANT TESTING 



In the operation of the apparatus the pinchcocks Ci and C 2 are opened and 
water which has been thoroughly saturated with the kind of gas to be 
analyzed is poured into the leveling tube until both tubes are about 

half full. Now raise the leveling tube L 
so that the water from it flows into the 
burette B, making it entirely full. The 
pinchcock Ci should now be closed and 
connect the rubber capillary tubing at 
the pinchcock to the pipe from which 
the gas for analysis is to be taken. 
After connecting to the gas pipe again 
open the pinchcock Ci and draw a little 
more than 100 cubic centimeters of gas 
into the burette. Allow the apparatus 
to stand a minute in this position to per- 
mit the water clinging to the sides of the 
burette to drain. Now close the pinch- 
cock Ci and by raising the leveling tube 
compress the gas in the burette until the 
meniscus stands at the 100 cubic centi- 
meter mark, close the pinchcock C 2 on 
the lower length of rubber tubing and 
open the pinchcock Ci at the top of the 
burette momentarily to release the pres- 
sure in it. During this adjustment hold the leveling tube so that the 
surface of the water in it is on the same level as in the burette. There 
will be exactly 100 cubic centimeters 
of gas in the burette at atmospheric 
pressure if, when the pinchcock Ci is 
opened, the meniscus remains at the 
100 mark. If, however, the meniscus 
shifts from the 100 mark, the adjust- 
ment will have to be repeated. 

Constituents of the gas must be 
absorbed in the following order: (1) 
carbon dioxide (C0 2 ) with potassium 
hydrate (KOH) 1 or sodium hydrate 
(NaOH) ; (2) " illuminant hydrocar- 
bons " (ethylene C2H2, and benzine 
C 6 H 6 in combination) with saturated bromine water 2 or fuming sulphuric 

1 These reagents are the same as used in the flue gas apparatus. 

2 Power Test Committee of A.S.M.E. specified bromine water for the hydrocarbons 
and NaOH for CO2. NaOH is cheaper than KOH but the latter is the more rapid 
absorbent. 




Fig. 285. — Hempel Gas Apparatus. 




Fig. 286. — Explosion Pipette. 



FLUE GAS ANALYSIS 247 

acid; (3) oxygen (0 2 ) with caustic pyrogallic acid; (4) carbon monoxide 
(CO) with cuprous chloride; (5) marsh gas or methane (CH 4 ), hydrogen 
(H 2 ) and nitrogen (N 2 ). 

A pipette must be provided for each of the reagents and those for 
pyrogallic acid and cuprous chloride which absorb oxygen must be pro- 
vided with water seals. Both ends of the pipette for fuming sul- 
phuric acid must be kept closed except when an absorption is being 
made. 

After the sample has been collected in the burette the latter is at- 
tached to an absorption pipette as shown in Fig. 285 by a short piece of 
bent glass capillary tubing. Before this attachment is made the glass 
capillary should be filled with water by means of a medicine dropper, 
so as to avoid the error of entrapping air in this tubing. The pinch- 
cock Ci should now be open and by raising the leveling tube all the gas 
should be forced over into the pipette until the water from the burette 
fills the glass capillary connecting tube. Now close the pinchcock Ci 
and shake the pipette lightly to give the gas the best sort of contact 
with the absorption reagent. After shaking for two or three minutes 
the gas should be drawn back into the burette by lowering the leveling 
tube until the solution from the pipette fills the connecting capillary 
tube when the pinchcock Ci should be closed. The surfaces of the water 
in the leveling tube and in the burette should now be brought to the 
same level. The reading on the scale observed after draining the burette 
for two minutes as read at the bottom of meniscus should be recorded. 
The process must be repeated as in the operation of an apparatus for flue 
gas analysis until the reading is constant. In this way by the use of 
the proper pipettes all the constituents of the gas to be analyzed, with 
the exception of H 2 and CH 4 , are determined. 

Explosion Tests. For determining hydrogen and marsh gas (CH 4 ) 
combustion tests are made in a pipette like Fig. 286 which is made par- 
ticularly strong for exploding gases over mercury. In the upper portion of 
the pipette A there are two very fine platinum wires which are fused into 
the glass from opposite sides. When the spark from an induction coil 
is made to pass through the air gap between the two wires the explosive 
mixture contained is ignited. The explosion takes place with consider- 
able force so that extreme precautions should be taken to observe that 
the glass cock C and a very strong screw type of pinchcock at the end of 
the capillary tube U are very firmly closed. It is also very desirable to 
hold a wire screen about a foot square between the operator and the 
pipette when the spark is made and the explosion occurs. 

Procedure for the explosion pipette is as follows: Measure about 
15 cubic centimeters (call this m) of the n cubic centimeters of gas 
remaining after the absorption of CO by the cuprous chloride and put 



248 POWER PLANT TESTING 

the gas remaining in the burette into the pipette for absorbing CO. 
Now transfer these 15 cubic centimeters to the explosion pipette and 
immediately thereafter measure about 85 cubic centimeters of air and 
add this to the gas in the explosion pipette. Then after closing both cocks 
very carefully and tightly and shaking lightly to insure a good mixture, 
close the electric circuit momentarily through the induction coil to cause 
the explosion. After the explosion, and allowing a little time for cooling, 
measure the gas in the burette. Then pass the same gas into the C0 2 
pipette, measure the absorption of CO2 in the burette, call this V cubic 
centimeters, and finally pass the remainder into the 2 pipette and deter- 
mine the volume of oxygen remaining. 

In the explosion the following reactions took place: 
2H 2 + 2 = 2H 2 0. 
CH 4 + 20 2 = C0 2 + 2H 2 0. 

/ If y is the number of cubic centimeters of oxygen absorbed after the 
explosion, then since there are 20.8 per cent of oxygen by volume in air, 
and if x cubic centimeters of air were used to make the explosive mixture, 
the oxygen supplied is 0.208 x, and the oxygen used in the explosion is 
0.208 x — y. Assuming the water is all condensed and has practically no 
volume, the equations above show as regards volumes, 

Contraction of volume of gas (z) = § H 2 + 2 CH 4 . . . . (85) 

Oxygen used (0.208 x - y) = \ H 2 + 2 CH 4 (86) 

C0 2 formed (v) = CH 4 . 

Subtracting equation (86) from (85), 

z — [0.208 x — y] = H 2 (in m cu. cm. of " residual " gas), 

and total H 2 in original sample = — \z — [0.208 x — y]\. 

Similarly CH 4 in m cubic centimeters of " residual " gas is the absorption 

nv 

of C0 2 (v) and the total CH 4 in original sample is — ■ . 

Volume of nitrogen N can then be obtained by subtracting the sum of 
all the constituents now determined from the original volume of the 
sample of gas. Calculation of nitrogen content is, however, a good check 
on the accuracy of the analysis. Thus if, as above, x cubic centimeters 
of air were mixed with the m cubic centimeters of " residual " gas for the 
explosion test, then 0.208 x was oxygen and (x — 0.208 x) was nitrogen. 
After the C0 2 and 2 were absorbed from the products of the explosion 
there were say w cubic centimeters of nitrogen remaining, so that the 
m cubic centimeters of "residual " gas contained w — (x — 0.208 x) 
of nitrogen. Nitrogen content of the original sample is therefore 

- [w - x(l - 0.208)]. 



FLUE GAS ANALYSIS 249 

Results of the analysis should be tabulated and the accuracy as regards 
the " nitrogen check " stated clearly. 

Coefficient of Dilution. The coefficient of dilution is the ratio of the 
volume of the air supplied to the volume theoretically necessary to 
provide the oxygen required for combustion. It will now be shown how 
this coefficient can be calculated from an analysis of the flue gases. 

Oxygen when combining with carbon to form carbon dioxide pro- 
duces a volume equal to itself, thus, 

C + 2 = C0 2 , (74) 

and in forming carbon monoxide produces twice the volume 

2 C + 2 = 2 CO (75) 

Now if we use symbols to designate the percentages by volume of the 
gases in a sample of flue gas as follows: 

a is the percentage by volume CO2, 

b is the percentage by volume 2 , 

c is the percentage by volume CO, 

d is the percentage by volume N 2 (nitrogen). 

Then the volume occupied by the free oxygen in the air before com- 
bining with the carbon was a + b + \ c per cent, while that required 
for complete combustion is obviously a + c per cent. 

The coefficient of dilution 1 is therefore, 

*-W- <*» 

1 This coefficient is variously defined so that in stating a result the method of com- 
putation should be given. Many engineers write it thus: 

a +b + \ c 

x = ' 

a + \c 

where the denominator as given is the air required for the kind of combustion as indi- 
cated by the analysis. 

Another method sometimes used is based on the nitrogen content. Practically all 
the nitrogen indicated by the analysis is due to the total air supplied, and using d for 
the percentage of nitrogen we can write for the nitrogen which was a part of that used 
for combustion, approximately, 

d - 11 (& - I c), 
d 

and x = j W7Z TV 

d - Ir (& - i c) 

This last formula is not as accurate as any of the others, giving usually results about 
10 per cent too low. A better method than the last, based on the fact that the air 
supplied contains 20.8 per cent by volume of oxygen, is stated thus, 

_ 20.8 
X ~ 20.8 - b ' 



250 POWER PLANT TESTING 

In a little different form the reactions given in the last paragraph may 
be stated (1) for carbon burned to C0 2 , 

2 C + 2 2 = 2 C0 2 , (77) 

(solid) (2 vols.) (2 vols.) 
24 64 88 

and (2) for carbon burned to CO, 

2 C + 2 = 2 CO (78) 

(solid) (1 vol.) (2 vols.) 
24 32 56 

The ratio of the theoretical volume of the carbon burned to C0 2 , to the 
volume burned to CO is the same as the ratio of the volume of C0 2 in 
the products of combustion is to the volume of CO. Further since the 
ratio of volumes of the carbon vapor is obviously the same as the ratio 
of the corresponding weights, we may say that in a mixture of gases 
the ratio of the weight of carbon required to produce the C0 2 to the 
weight needed for the CO is equal to the ratio of the volume of C0 2 
in the mixture to the volume of CO. 

The atomic weights of carbon and oxygen" show (equation (77)) that 
the volume of oxygen is 2| (64/24) times as heavy as an equal volume of 
carbon vapor. It follows then that for burning one pound of carbon to 
C0 2 , 2f pounds of oxygen are required. The other reaction (78) show- 
ing the combination of carbon and oxygen to form CO shows with the 
same reasoning that If pounds of oxygen are required to burn one pound 
of carbon to CO. 

In the general case we are considering and using symbols a and c re- 
spectively as before to represent the volumes of C0 2 and of CO in the 
flue gases, then the weight of the carbon burned to C0 2 is to the weight 

burned to CO as a is to c and if represents the weight of carbon 

a ~\~ c 

burned to C0 2 and the weight burned to CO, then the weight of 

a -\- c 

oxygen required per pound of carbon is 2§ ( — ~— J + i| f — — J and the 
weight of air 1 per pound of carbon is in pounds, 

K-r-cHfe)] m 



100 r_ 

If z is the percentage by weight of carbon in the coal then the weight 
of air in pounds per pound of coal is 
100 z I 

1 Weight of air may be checked with Peabody's and Jacobus' equations (86, 87, 
and 88), pages 281 and 283. 



K-f>*(aT-c)] <» 



FLUE GAS ANALYSIS 251 

Volumetric analyses of the flue gases can be used also to calculate the 
weight of the products of combustion (flue gases) per pound of coal 
burned and also the heat units lost in these gases. For this calculation 



the relations of the molecular weights are important. 

Molecular weight of C0 2 = 44; 2 = 32; CO = 28; N 2 = 28; 
C = 12. 

Now in a sample of x pounds of flue gases in which the percentages 
by volume are represented by the symbols a, b, c, d, the relative per- 
centages by weights of the constituents will be 

nr . 44 a _ 32 6 __ 28 c AT 28 d , ., , ,, 

C0 2 = ; 2 = ; CO = ; JN 2 = ; and we can write further 

x x x x 

Weight of carbon burned to C0 2 in x pounds of gas = \\ X 44 a = 12 a. 
Weight of carbon burned to CO in x pounds of gas = $f X 28 c = 12 c. 
Total weight of carbon burned in x pounds of gas = 12 (a + c). 

Total weight of carbon burned per pound of gas = 12 • 

Total weight of gas generated per pound of carbon = -^ — — - - • 

i.Z \Cb -\- c) 

Of this total weight of gas as expressed by the last equation the con- 
stituents are distributed in percentages by weight as follows : 
Weight of C0 2 in samples per pound carbon burned, 

44 ax 



w\ 


12 x (a + c)' 


co 2 


tea 


~ Wl ~ 12 (a + c) 


2 


32 6 


W2 12 (a + c) 


CO 


28 c 


Ws 12 (a + c) 


N 2 


28 c? 



or we may write 

lb.; 

14 ya -|- c) 
and similarly, 

lb. 

lb. 

12 (a + c) lb ' 

Total weight of gases w g per pound of coal burned, if there is z per 
cent 1 of carbon in the coal, is in pounds 

z (44 a + 32 b + 28 c + 28 d) , Q , 

w '~ 12 (a + c) 100 (8l) 

Now if we represent by t f and t a the temperatures respectively in 
degrees Fahrenheit of the gases in the flue and of the air entering the 

1 It may be assumed for very approximate values that z = 1 — y where y is the per 
cent of ash and moisture in the coal. 



252 POWER PLANT TESTING 

furnace, then the heat lost in the flue gases Q g per pound of coal is, 
inserting values of specific heats, 1 

Q g = —^(.217 W! + .217 w 2 + .245^3 + .244 Wi ) (t, - t a ). 

The total heat generated Qo by the more or less incomplete com- 
bustion of one pound of coal when there are a and c percentages by 
volume respectively of C0 2 and CO in the flue gas is 

Qo = ^(— ^xi4,600 + -4-xMooWt.u.), • • ( 82 ) 

100 \a + c a + c / 

since the heat of combustion of carbon when burned to C0 2 is approxi- 
mately 14,600 and when burned to CO is about 4400 B.t.u. 

Finally, if Q p is the heat from perfect combustion or the " calorific " 
value in B.t.u. of a pound of coal, then the efficiency of the furnace 2 = 

~ . The percentage of heat from perfect combustion lost in the flue 

Q g 

gases = jf> 

Recording Apparatus for Determining C0 2 . A typical apparatus 
for making a continuous record of the percentage by volume of carbon 
dioxide in gases is shown in Fig. 287. 3 The gas is taken to the instrument 
from the side flue or last combustion chamber of each boiler or furnace to 
the inlet pipe D and is drawn through the machine by a special water 
aspirator Q, fixed to the top of the instrument by means of the standard 
T. After actuating the aspirator Q, a portion of the water flows to the 
small tank L, which serves as a pressure regulator, and is provided with 
an overflow tube R. From this tank the water enters the. tube H in a 
fine stream, which is adjusted by the cock S and gradually fills the 
vessel K. This vessel consists of an upper and a lower compartment, 
the two being in communication through a tube erected in the upper 
chamber and reaching nearly to the top. Water, which enters this 
vessel K through the tube H, gradually fills the upper chamber and 
thus compresses the air contained in it. This pressure is transmitted to 
the lower compartment through the communication tube mentioned 
above, and acts upon the mixture of glycerine and water with which this 
is filled, driving it out into the calibrated tube C. When the rising liquid 
in C has reached the inlet and outlet to this vessel, no more gas can enter 

1 This method of finding the heat escaping in the flue gases may be used to correct 
determinations made with the Junkers calorimeter (page 224) when the products of 
combustion are discharged at a temperature different from that of the room. 

2 For the calculation of related quantities see "Heat Balance " (A.S.M.E. Rules), 
pages 280 and 281. 

3 Sarco Engineering Co., West Street, N. Y. 



FLUE GAS ANALYSIS 



253 



the calibrated tube and the aspirator will now draw the gas through 
the seal F. 

Before the liquid can close the central tube in C, the gas must over- 
come the slight resistance offered by the elastic bag P, and is thereby 
forced to assume atmospheric pressure. 
When the liquid has sealed the lower open 
end of this central tube, exactly 100 cubic 
centimeters of flue gas are trapped off in 
the outer vessel C and its companion tube, 
under atmospheric pressure. As the liquid 
rises, the gas is forced through the thin 
tube Z into the vessel A, which is filled 
with a solution of caustic potash for ab- 
sorbing carbon dioxide. 

The gas remaining gradually displaces the 
potash solution in A, sending it up into the 
vessel B. This has an outer jacket filled 
with glycerine and supports a float N. 
Through the center of this float reaches a 
thin tube, through which the air in B is 
kept at atmospheric pressure. The float is 
suspended from the pen gear M by a silk 
cord and counterbalanced by the weight X. 
The liquid in B forces a portion of the air 
through the central tube in the float, and 
then raises the latter, causing the pen lever 
to swing upward, carrying the pen Y with it. 

The mechanism is so calibrated and ad- 
justed that the pen will travel to the top, 
or zero line, on the chart when only atmospheric air is passing through 
the machine, and nothing is absorbed by the potash in A. When there 
is any carbon dioxide in the gas it is absorbed by the potash in A, and 
not so much of this liquid would be forced up into the vessel B. The 
float would not then cause the pen to travel up so high on the chart, in 
proportion to the amount of C0 2 absorbed. 

" Precision " Simmance-Abady C0 2 Recorder 1 (Fig. 288) is a most 
satisfactory instrument, being at the same time simple and accurate. 
Through the valve V a continuous flow of water is maintained into the 
chamber k, with an overflow through o. Some of this water flows 
through E into the tank A and the float F rises with the water level. 
As it rises the cylinder d falls since they are joined by a cord c. When 
F is at the top of its stroke it raises a valve stem S, trips the valve and 
1 Precision Instrument Co., Detroit. 




— Recording C0 2 
Apparatus. 



254 



POWER PLANT TESTING 



causes the water in A to be siphoned out through the tube g. This 
lowering of the water level permits the float F to be lowered and at 
the same time raises the cylinder d, making a partial vacuum under it. 

Chimney gases are thus drawn from the 
flues into this bell through a supply pipe P. 
The water discharged from the tube g 
into the cup U when it overcomes the 
counterweight W, closes the valve h in 
the pipe P, and entraps a fixed volume of 
gas below d. In the meantime water has 
been continuously flowing into A, causing 
F to rise again and d to drop as before. 
As d goes down the entrapped flue gas is 
forced by means of the small pipes shown 
through the KOH solution in M and 
then into the " recorder " chamber R 
which is also water sealed by a cylinder 
j. Displacement of the cylinder j will be 
less in proportion to the volume of gas 
(C0 2 ) absorbed. The elevation to which j 
rises is indicated on a scale N graduated in 
per cent of C0 2; and a very simple record- 
ing device not shown in the figure regis- 
ters on a chart corresponding values. 
Samples are analyzed and records made 
every three minutes. A branch of the gas pipe P goes to Q where it 
enters a small water aspirator supplied with water from the pipe V 
which is continuously exhausting gas from the flues so that the sample 
entering the instrument shows its true analysis when it was taken. 

Uehling's C0 2 Recorder or " Composimeter m is shown diagram- 
matically in Fig. 289. The gas to be analyzed is drawn through the two 
apertures at A and B by a constant suction produced by an aspirator. 
If these apertures are kept at the same temperature, the suction or 
partial vacuum in the chamber between the two apertures will remain 
constant so long as all the gas passes through both apertures ; if, however, 
part of the gas be taken away or absorbed in the space between the 
apertures the vacuum will increase in proportion to the amount of gas 
absorbed. It is evident that if a manometer or light vacuum gage be 
connected with this chamber, the amount of gas absorbed will be indi- 
cated by the vacuum reading. 

The diagram shows the more important parts of the instrument. 
Gas is drawn from the last pass or uptake of the boiler by means of the 
1 Uehling Instrument Co., Passaic, N. J. 




Fig. 288. — "Precision' 
corder. 



C0 2 Re- 



FLUE GAS ANALYSIS 



255 



To CO? "Recorder 



Absorption Chamber 
A 



aspirator through a preliminary filter located at the boiler, then through 
a second filter on the instrument as shown, and finally it passes through 
aperture A, the absorption chamber, and aperture B, to the aspirator, 
where it leaves the instrument with 
the exhaust steam. 

The C0 2 is completely absorbed 
by the caustic solution as the gas 
flows through the absorption cham- 
ber located between apertures A and 
B. Its volume will be reduced which 
causes a change in the tension (par- 
tial vacuum) of the gas between the 
two apertures. This tension varies 
with the percentage of C0 2 contained 
in the gas, and is indicated by a 
water column at the instrument, and 
by a recording vacuum gage gradu- 
ated to read percentages of C0 2 . 

Another apparatus for making con- 
tinuous determinations of C0 2 in flue 
gases is shown in Fig. 290. Gas from 
the boiler flue enters at M, passes 
through an excelsior filter where dust 
is removed, and then goes on through 
tubes leading it through glass vessels 

containing cotton wool and calcium chloride. After being cleaned and 
dried it passes in the direction of the arrows through the valve B into 
the weighing apparatus. On account of the greater specific gravity of 
C0 2 the larger the percentage of this gas the greater the tendency will 
be to pull downward the vessel G so that the pointer S on the balance 
can be adjusted to make the scale over which it travels indicate the per- 
centage of C0 2 . For such a method of determination, obviously, the 
gas must be clean and dry. The cleaning is done by the excelsior and 
wool filters and the drying is done by the calcium chloride. 

Smoke Determinations. The method most generally used to de« 
termine the density of smoke is with a Ringelmann chart, which is shown 
in reduced scale in Fig. 291. Cards ruled like those shown, but 
covering a much larger area, are placed in a horizontal row about 50 
feet from the observer and in line with the chimney, together with plain 
white and black cards. The observer glances rapidly from the chimney 
to the cards and judges which one corresponds most nearly with the color 
of the smoke. The lines in cards 1 to 4 are respectively 1, 2.3, 3.7 and 
5.5 millimeters thick and the spaces are 9, 7.7, 6.3, and 4.5 millimeters. 




Gas "Composi- 



256 



POWER PLANT TESTING 



c h 




M pg From Boiler Flue 



Fig. 290. — C0 2 "Weighing" Apparatus (Econometer), 

A soot collecting method is sometimes used. It is applied by sus- 
pending by a wire from the top of the flue a plate f-inch wide and 24 
inches long. The hole through which the plate is inserted is kept 
covered at other times. This plate is temporarily withdrawn every 
two hours and the collection of soot removed and weighed. 





■ 




■ 




■ 






■ 


















n 




































■ 




































■ 


















■ 


















■ 


















■ 


















■ 



















No.3 



~No.l No.2 

Fig. 291. — Ringelmann Smoke Chart. 



No.4 



In another apparatus adopted by the Chicago Commerce Association 
a continuous sample of gas is drawn from the chimney by means of a 
special Pitot tube and exhauster. Solid particles in the gas collected 
are entrapped in a filter. The collecting tube is so arranged that the 
rate of flow through the apparatus is the same as that through the 



FLUE GAS ANALYSIS 257 

chimney, so that when applied to chimneys of different areas the weight 
of soot, etc., collected is a measure of the density of the smoke. 

Eddy Smoke Recorder 1 is one of the few devices for automatically 
recording the density of smoke. The apparatus consists in its latest 
form of a steam ejector which draws a continuous flow of gas from the 
chimney and discharges it through a nozzle against a paper-covered 
drum revolved by a clock mechanism. The soot in the smoke makes 
its own record on the chart. 

1 Hamler-Eddy Co., Chicago. 



CHAPTER X 

INSTRUCTIONS REGARDING REPORTS OF TESTS IN GENERAL 1 

Object. Ascertain the specific object of the test, and keep this in view 
not only in the work of preparation, but also during the progress of the 
test, and do not let it be obscured by devoting too close attention to 
matters of minor importance. Whatever the object of the test may be, 
accuracy and reliability must underlie the work from beginning to end. 

If questions of fulfillment of contract are involved, there should be 
a clear understanding between all the parties, preferably in writing, as 
to the operating conditions which should obtain during the trial, and as 
to the methods of testing to be followed, unless these are already ex- 
pressed in the contract itself. 

Among the many objects of performance tests, the following may be noted: 

Determination of capacity and efficiency, and how these compare with stand- 
ard or guaranteed results. 

Comparison of different conditions or methods of operation. 
Determination of the cause of either inferior or superior results. 
Comparison of different kinds of fuel. 

Determination of the effect of changes of design or proportion upon capacity 
or efficiency, etc. 

Dimensions. Measure the dimensions of the principal parts of the 
apparatus to be tested, so far as they bear on the objects in view, or 
determine these from correct working drawings. Notice the general 
features of the same, both exterior and interior, and make sketches, if 
needed, to show unusual points of design. 

The dimensions of the heating surfaces of boilers and superheaters 
to be found are those of surfaces in contact with the fire or hot gases. 2 
The submerged surfaces in boilers at the mean water level should be 
considered as water-heating surfaces, and other surfaces which are 
exposed to the gases as superheating surfaces. 

In the case of condensers, feedwater heaters, and the like, the outside surfaces 
are to be taken. In reheaters and steam jackets, the surfaces to be considered 
are those exposed to the steam of lower pressure. 

The dimensions of engine cylinders should be taken when they are cold, and, 

1 Report of Committee on Power Tests, Journal of American Society of Mechanical 
Engineers, Nov., 1912. 

2 Heating surface in fire-tube boilers is therefore calculated on the basis of the in- 
side diameter of the tubes. 

258 



REPORTS OF TESTS IN GENERAL 259 

if extreme accuracy is required, as in scientific investigations, corrections should 
be applied to conform to the mean working temperature. If the cylinders are 
much worn, the average diameter should be found. Clearance of the cylinders 
may be determined approximately from working drawings of the engine. For 
accurate work, when practicable, the clearance should be determined by the 
water measurement method. (See page 293.) 

Examination of Plant. Make a thorough examination of the physical 
condition of all parts of the plant or apparatus which concern the object 
in view, and record the conditions found, together with any points in 
the matter of operation which bear thereon. 

Boiler Leakage. In boilers, for example, examine for leakage of tubes and riveted 
or other metal joints. Note the condition of brick furnaces, grates and baffles. 
Examine brick walls and cleaning doors for air leaks, either by shutting the 
damper and observing the escaping smoke 1 or by candle-flame test. Determine 
the condition of heating surfaces with reference to exterior deposits of soot and 
interior deposits of mud or scale. 

See that the steam main or header is so arranged that condensed and entrained 
water cannot flow back into the boiler. 

Ascertain the interior condition of all steam, air, gas, or water cylinders and 
the condition of their pistons, and of water plungers and impellers, together with 
the valves and valve-seats belonging thereto. Locate vacuum leaks in ex- 
haust piping, condenser, packings, etc., using vacuum gage or candle-flame 
test. Examine steam, air, gas, or water piping, traps, drip valves, blow-off 
cocks, safety valves, relief valves, heaters, etc., and make sure that they do not 
leak. Determine the condition of the blading, nozzles, and valves in steam 
turbines, and of buckets, guides and draft-tubes in water turbines. 

If the object of the test is to determine the highest efficiency or ca- 
pacity obtainable, any physical defects, or defects of operation, tending 
to make the result unfavorable should first be remedied ; all fouled parts 
being cleaned, and the whole put in first-class condition. If, on the 
other hand, the object is to ascertain the performance under existing 
conditions, no such preparation is either required or desired. 

General Precautions against Leakage. In steam tests make sure that 
there is no leakage through blow-offs, drips, etc., or any steam or water 
connections of the plant or apparatus undergoing test, which would in 
any way affect the results. All such connections should be blanked off, 
or satisfactory assurance should be obtained that there is leakage neither 
out nor in. This is a most important matter, and no assurance should 
be considered satisfactory unless it is susceptible of absolute demon- 
stration. 

Apparatus and Instruments. Select the apparatus and instruments 
specified in the Code of Rules 2 applying to the test in hand, locate and 
install the same, and complete the preparations for the work in view. 

1 Test for air leaks in the setting by firing a few shovelsful of smoky fuel and by 
immediately closing the damper, observing the escape of smoke through the crevices. 

2 Various codes are given in this book, beginning on page 269. 



260 POWER PLANT TESTING 

The arrangement and location of the testing appliances in every case 
must be left to the judgment and ingenuity of the engineer in charge, 
the details being largely dependent upon locality and surroundings. 
One guiding rule, however, should always be kept in view, viz., see that 
the apparatus and instruments are substantially reliable, and arrange 
them in such a way as to obtain correct data. 

A summary is given below, embracing the entire list of apparatus and 
instruments referred to in the various Codes, with descriptions of their 
leading features, methods of application and use, and, where needed, 
methods of calibration. 

(a) Weighing Scales. For determining the weight of coal, oil, water, etc., ordinary 
platform scales serve every purpose. Too much dependence, however, should 
not be placed upon their reliability without first calibrating them by the use of 
standard weights, and carefully examining the knife-edges, bearing plates, and 
ring suspensions, to see that they are all in good order. 

Other scales required in connection with test work are small scales for weigh- 
ing coal-samples used in drying, and laboratory scales for analysis and calorific 
determinations pertaining to fuels. Such scales should be sensitive to 1/1000 
of the quantity weighed. 

For testing locomotives and some classes of marine boilers, where room is 
lacking, sacks or bags are sometimes required to facilitate the handling of coal, 
the sacks being previously weighed at the time of filling. 

(a) Leakage. 

It is not always necessary to blank off a connecting pipe to make sure that there is 
no leakage through it. If satisfactory assurance can be had that there is no chance for 
leakage, this is sufficient. For example, where a straightway valve is used for cutting 
off a connecting pipe, and this valve has double seats with a hole in the bottom be- 
tween them, this being provided with a plug or pet cock, assurance of the tightness of 
the valve when closed can be had by removing the plug or opening the cock. Like- 
wise, if there is an open drip pipe attached to an unused or empty section of pipe 
beyond the valve, the fact that no water escapes here is sufficient evidence of the tight- 
ness of the valve. The main thing is to have positive evidence in regard to the tight- 
ness of the connections, such as may be obtained by the means suggested above; but 
where no positive evidence can be obtained, or where the leakage that occurs cannot 
be measured, it is of the utmost importance that the connections should be broken 
and blanked off. 

Leakage of relief valves which are not tight, drips from traps, separators, etc., and 
leakage of tubes in the feed-water heater must all be guarded against or measured and 
allowed for. 

It is well, as an additional precaution, to test the tightness of the feed-water pipes 
and apparatus concerned in the measurement of the water by running the pump at a 
slow speed for, say, fifteen minutes, having first shut the feed valves at the boilers and 
making sure they are tight. Leakage will be revealed by disappearance of water from 
the supply tank. In making this test a gage should be placed on the pump discharge to 
guard against undue or dangerous pressure. 

(b) Water-glass Tests of Leakage. 

To determine the leakage of steam and water from a boiler and steam pipes, etc., 
the water-glass method may be satisfactorily employed. This consists of shutting off 



REPORTS OF TESTS IN GENERAL 261 

all the feed valves (which must be known to be tight) and the main feed valve, thereby 
stopping absolutely the entrance or exit of water at the feed pipes to the boiler; then 
maintaining the steam pressure (by means of a very slow fire) at a fixed point, which 
is approximately that of the working pressure, and observing the rate at which the 
water falls in the gage glasses. It is well, in this test, as in other work of this char- 
acter, to make observations every ten minutes, and to continue them for such length 
of time that the differences between successive readings attain a constant rate. In 
many cases the conditions will have become constant at the expiration of fifteen min- 
utes from the time of shutting the valves, and thereafter the fall of water due to leak- 
age of steam and water become approximately constant. It is usually sufficient, after 
this time, to continue the test for two hours, thereby obtaining a number of half-hourly 
periods. When this test is finished, the quantity of leakage is ascertained by calcu- 
lating the volume of water winch has disappeared, using the area of the water level and 
the depth shown on the glass, making due allowance for the weight of one cubic foot 
of water at the observed pressure. The water columns should not be blown down 
during the time a water-glass test is going on, nor for a period of at least one hour 
before it begins. 

If there is opportunity for condensation to occur and collect in the steam pipe dur- 
ing the leakage test, the quantity should be determined as closely as desirable, and 
properly allowed for. 

(c) Piston Rod and Valve Rod Leakage. 

In making an engine test where the steam consumption is determined from the 
amount of water discharged from a surface condenser, leakage of the piston rods and 
valve rods should be guarded against; for if these are excessive the test is of little use, 
as the leakage consists partly of steam that has already done work in the cylinder and 
of water condensed from the steam when in contact with the cylinder. If such leak- 
age cannot be prevented, some allowance should be made for the quantity thus lost. 
The weight of water as shown at the condenser must be increased by the quantity 
allowed for this leakage. 



MISCELLANEOUS INSTRUCTIONS 

The person in charge of a test should have the aid of a sufficient 
number of assistants, so that he may be free to give special attention to 
any part of the work whenever and wherever it may be required. He 
should make sure that the instruments and testing apparatus con- 
tinually give reliable indications, and that the readings are correctly 
recorded. He should also keep in view, at all points, the operation of 
the plant or part of the plant under test and see that the operating con- 
ditions determined on are maintained and that nothing occurs, either 
by accident or design, to vitiate the data. This last precaution is 
especially needed in guarantee tests. 

Before a test is undertaken, it is important that the boiler, engine, or 
other apparatus concerned, shall have been in operation a sufficient 
length of time to attain working temperatures and proper operating 
conditions throughout, so that the results of the test may express the 
true working performance. 



262 POWER PLANT TESTING 

It would, for example, be manifestly improper to start a test for determining the 
maximum efficiency of an externally fired boiler with brick setting, until the 
boiler had been at work a sufficient number of days to dry out thoroughly and 
heat the brick work to its working temperature; and likewise improper to be- 
gin an engine test for determining the performance under certain prearranged 
conditions until those conditions had become established by a suitable prelimi- 
nary run. 

An exception should be noted where the object of the test is to obtain 
the working performance, including the effect of preliminary heating in 
which case all the conditions should conform to those of regular service. 

In preparation for a test to demonstrate maximum efficiency, it is 
desirable to run preliminary tests for the purpose of determining the most 
advantageous conditions. 

In all tests in which the object is to determine the performance un- 
der conditions of maximum efficiency, or where it is desired to ascertain 
the effect of predetermined conditions of operation, all such conditions 
which have an appreciable effect upon the efficiency should be main- 
tained as nearly uniform during the trial as the limitations of practical 
work will permit. In a stationary steam plant, for example, where 
maximum efficiency is the object in view, there should be uniformity in 
such matters as steam pressure, times of firing, quantity of coal supplied 
at each firing, thickness of fire, and in other firing operations; also in 
the rate of supplying the feed-water, in the load on the engine or tur- 
bine, and in the operating conditions throughout. On the other hand, 
if the object of the test is to determine the performance under working 
conditions, no attempt at uniformity is either desired or required unless 
this uniformity corresponds to the regular practice and when this is 
the object the usual working conditions should prevail throughout the 
trial. 

A log of the data should be entered in notebooks or on blank sheets 
suitably prepared in advance. This should be done in such manner that 
the test may be divided into hourly periods, or if necessary, periods of less 
duration, and the leading data obtained for any one or more periods 
as desired, thereby showing the degree of uniformity obtained. •' 

The readings of the various instruments and apparatus concerned in 
the test other than those showing quantities of consumption (such as 
fuel, water, and gas) should be taken at intervals not exceeding half an 
hour and entered in the log. Whenever the indications fluctuate, the 
intervals should be reduced according to the extent of the fluctuation. 
In the case of smoke observations, for example, it is often necessary to 
take observations every minute, or still oftener, continuing these through- 
out the period covering the range of variations. 

Make a memorandum of every event connected with the progress of a 
test, however unnecessary at the time it may appear. A record should 



REPORTS OF TESTS IN GENERAL 263 

be made of the exact time of every such occurrence and the time of tak- 
ing every weight and every observation. For the purpose of identi- 
fication the signature of the observer and the date should be affixed 
to each log sheet or record. 

In the simple matter of weighing coal by the barrow-load, or weighing 
water by the tank-full, which is required in many tests, a series of marks, 
or tallies, should never be trusted. The time each load is weighed or 
emptied should be recorded. The weighing of coal should not be dele- 
gated to unreliable assistants, and whenever practicable, one or more 
men should be assigned solely to this work. The same may be said 
with regard to the weighing of feedwater. 

To show the uniformity of the data at a glance the whole log of the 
trial should be plotted on a chart, using horizontal distances to represent 
times of observation, and vertical distances on suitable scales to repre- 
sent various data as recorded. Such a chart showing the log of a boiler 
test is illustrated in Fig. 296, page 268. 

It is very heplful to plot the leading data on such a chart while the 
test is in progress. 

Report of a test should present all the leading facts bearing on the 
design, dimensions, condition, and operation of the apparatus tested, 
and should include a description of any other apparatus and auxiliaries 
concerned, together with such sketches as may be needed for a clear 
understanding of all points under consideration. It should state clearly 
the object and character of the test, the methods followed, the conditions 
maintained, and the conclusions reached, closing with a tabular summary 
of the principal data and results. . 

The standard units on which to base the various measures of capacity 
and the standard forms of expressing efficiency and economy to which 
the codes apply are as follows: 

STANDARD UNITS OF CAPACITY 

a Boilers 1 f One pound of water evaporated into dry steam 

1 from and at 212 deg. F. per hour. 

(One indicated horse power developed in the 
main cylinders i.h.p. 

One brake horse power delivered by the main 
shaft b.h.p. 

c Steam Turbines f One brake horse power delivered by the main 

I shaft b.h.p. 

1 A subsidiary unit which may be used for stationary boilers is a " Boiler Horse 
Power," or 34| pounds of water evaporated from and at 212 deg. F. per hour, i.e., from 
water at 212 deg. F. into steam at the same temperature. Electrical engineers have 
suggested a unit termed " Myriawatt," which differs but little from boiler horse power 
when expressed in B.t.u. per hour. 



264 



POWER PLANT TESTING 



driven generators) 
Pumping Machinery. 



kw.-hr. 



1 One kilowatt-hour delivered at the busbar, 1 not 
\ I including exciter output 2 

One gallon of water discharged to the force 
main in 24 hours. 

One gallon of water discharged per min 3 gal. per min. 

One water horse power delivered to the force 
main, based on the total head including 
suction 



/ Air Machinery 

g Locomotives. . 

Gas Produce 

Gas and Oil Engines . 



w.h.p. 



F. and 30-in.' 



cu. ft. 
air h.p. 

i.h.p. 



One cu. ft. of air at 62 

barometer 

; One air horse power 

One indicated horse power developed in the 

main cylinders 

One dynamometer horse power delivered to 

the draw-bar dyn. h.p. 

h Gas Producers One pound of dry fuel consumed per hour 

(One brake horse power delivered by the main 

( shaft b.h.p. 



. w , . ( One brake horse power delivered by the main 

7 W aterwneels { i ^ , i i 

J I shaft b.h.p. 



STANDARDS OF EFFICIENCY AND ECONOMY 



a Boilers. 



6 Reciprocating Steam 
Engines 



c Steam Turbines . 



d Turbo-generators, 

(including engine- 
driven generators) . . 



Relation between B.t.u. absorbed by boiler 
coal fired and calorific value of 1 lb. coal, 
of boiler furnace and grate.) 

Relation between B.t.u. absorbed by boiler, 
combustible burned and calorific value of 
bustible. (Efficiency of boiler and furnace.) 

'(1) B.t.u. per i.h.p.-hr. 

(2) B.t.u. per brake h.p.-hr. 

(3) Thermal efficiency ratio referred to i.h.p. 

(4) Thermal efficiency ratio referred to b.h.p. 

(5) Lbs. of dry steam per. i.h.p.-hr. 

(6) Lbs. of dry steam per b.h.p.-hr. 
'(1) B.t.u. per b.h.p.-hr. 

(2) Thermal efficiency ratio. 

(3) Lbs. of dry steam per b.h.p.-hr. 

(1) B.t.u. per kw.-hr. 

(2) Thermal efficiency ratio. 

(3) Lbs. of dry steam per kw.-hr. 



per lb. of 
(Efficiency 

per lb. of 
1 lb. com- 



1 It is assumed that the drop in voltage between generator terminals and switch- 
board is not over one-half of one per cent. 

2 If the exciter current is taken from an outside source the kw. thus supplied are to 
be deducted from the total output. 

3 This unit applies to small pumps and some classes of large-sized pumps. 

4 30-in. barometer is referred to a temperature of 62 deg. F.; or 29.92-in. referred to 
32 deg. F. (see page 223). 



REPORTS OF TESTS IN GENERAL 



265 



Pumping Engines . 



/ Air Machinery . 



(1) Ft.-lbs. of work per million B.t.u. 

(2) Ft.-lbs. of work per 1000 lbs. dry steam. 

(3) Ft.-lbs. of work per 100 lbs. dry fuel. 
'(1) B.t.u. per net air h.p. per hr. 

(2) Lbs. of dry steam per net air h.p. per hr. 

(3) Lbs. of dry steam per 1000 cu. ft. of free air com- 
pressed to 100 lbs. gage pressure reduced to atmospheric 
temperature. 



Locomotives . 



h Gas Producers. 



i Gas and Oil Engines . 
j Waterwheels 



k Steam Power Plants. 



I Electric Power Plants . . - 



m Pumping Engine 
Plants 



Lbs. of dry fuel per i.h.p.-hr. 
Lbs. of dry fuel per dyn. h.p.-hr. 
Lbs. of dry steam per i.h.p.-hr. 
Lbs. of dry steam per dyn. h.p.-hr. 
Lbs. of dry fuel per ton-mile. 
Relation between B.t.u. of the gas output per lb. of fuel 
charged and calorific value of 1 lb. of fuel. 

(1) B.t.u. per brake h.p.-hr. 

(2) Thermal efficiency ratio referred to b.h.p. 

(3) Lbs. of dry fuel per b. h.p.-hr. 

(4) Cu. ft. of gas per b. h.p.-hr. 
| Relation between brake h.p. and potential h.p. of total 

water used. 
r (1) Lbs. of dry fuel per i.h.p.-hr., main engine. 

(2) Lbs. of dry fuel per i.h.p.-hr., auxiliaries. 

(3) Lbs. of dry fuel per i.h.p.-hr., whole plant. 

(4) Lbs. of dry steam per i.h.p.-hr., main engine. 

(5) Lbs. of dry steam per i.h.p.-hr., auxiliaries. 

(6) Lbs. of dry steam per i.h.p.-hr., whole plant. 
"(1) Lbs. of dry fuel per kw.-hr., main engine or turbine. 

(2) Lbs. of dry fuel per kw.-hr., auxiliaries. 

(3) Lbs. of dry fuel per kw.-hr., whole plant. 

(4) Lbs. of dry steam per kw.-hr., main engine or turbine. 

(5) Lbs. of dry steam per kw.-hr., auxiliaries. 

(6) Lbs. of dry steam per kw.-hr., whole plant. 

(1) Ft.-lbs. of work per million B.t.u. 

(2) Ft.-lbs. of work per 100 lbs. dry fuel. 

(3) Ft.-lbs. of work per 1000 lbs. dry steam. 
( (1) Lbs. of dry fuel per brake h.p.-hr. 
I (2) Cu. ft. of gas per b. h.p.-hr. 

The i.h.p. and b.h.p. in this table refer to that of the main engine, turbine, or 
waterwheel, and the kw. to the current measured at the busbar, not including exciter 
current. (See second footnote, page 264.) 

Contracts for power plant apparatus should specify the leading 
dimensions of the apparatus and its rated capacity, expressed in the 
units given in the table. If a specific guarantee of capacity is made, 
either working capacity or maximum capacity, the operating condi- 
tions under which the guarantee is to be met should be clearly set forth, 
such, for example, as steam pressure, speed, vacuum, quality of fuel, 
force of draft, etc. Likewise if a contract contains a guarantee of 
economy all the conditions should be fully specified. 



n Gas Power Plants. 



266 POWER PLANT TESTING 

Commercial Ratings. The commercial rating of capacity determined 
on for power plant apparatus, whether for the purpose of contracts, for 
sale, or otherwise, should be such that a sufficient reserve capacity beyond 
the rating is available to meet the contingencies of practical operation; 
such contingencies, for example, as the loss of steam pressure and capacity 
due to cleaning fires, inferior coal, oversight of the attendants, sudden de- 
mand for an unusual output of steam or power, etc. To secure this 
end, the following requirements should be met: 

(a) Boilers. The reserve capacity of a boiler should be at least one-third of the 
commercial rating, when using coal which is regarded as a standard where the 
boiler is located, the fire being crowded, and the draft between the damper and 
the boiler being at least ^-in. water column (draft gage) . 

A sufficient amount of grate surface should be provided in such a boiler to 
develop the rated capacity with the coal and draft named without crowding the 
fire. 

(b) Reciprocating Steam Engines and Steam Turbines. The reserve capacity of a 
steam engine or steam turbine at a stipulated steam pressure should be such as 
to allow a drop of at least 15 per cent in the pressure without material reduction 
in the normal speed at its rated capacity or load. It should also allow an over- 
load at the specified pressure amounting to at least 25 per cent of the rated 
power. 

(c) Pumping Engines. The reserve capacity of a pumping engine should be such 
as to permit a drop in the steam pressure of at least 15 per cent without sensible 
reduction in the quantity of water discharged at its rated capacity, and to al- 
low an increase in power sufficient to discharge 20 per cent more water than the 
rated amount. 

(d) Gas Producers. The reserve capacity of a gas producer should be such that 
when forced it will burn in a given time 20 per cent more coal of the quality 
agreed upon than the rated capacity. 

(e) Gas and Oil Engine^. The reserve capacity of an internal-combustion engine 
should be such that when supplied with gas of the kind and quality which it is 
designed to use, it should develop at least 20 per cent more power than the com- 
mercial rating. 

(/) Water wheels. The reserve capacity of a waterwheel should be at least 10 per 
cent more than the commercial rating at the specified head, the buckets in the 
wheel being clean and the flow of water unobstructed. 



CHAPTER XI 

BOILER TESTING 

Tests of steam boilers are made to determine usually the following 
principal results: 

(1) Quantity of steam evaporated or furnished per hour. 

(2) Efficiency as a heat user, or weight of water evaporated per pound 
of combustible (fuel less moisture and ash). 

(3) Weight of water evaporated per hour per square foot of water- 
heating surface. 

(4) Weight of fuel burned per hour per square foot of grate surface. 
Leakages of any kind are always a lurking enemy for those engaged in 

any kind of accurate testing, and work with boilers is no exception. 
Poor results with boilers are due more often to air leakage than to any 
other fault. Air entering the setting and flues instead of the furnace 
does not assist combustion, but, on the contrary, absorbs from the hot 
gases a quantity of heat which otherwise might pass through the boiler- 
heating surfaces into the water in the boiler. When the object of a series 
of tests is, for example, to compare one kind of coal with another, or one 
type of grate or mechanical stoker with another, the losses due to air 
leakage would not be of much consequence in what are only comparative 
results; but if a boiler is to give the best possible efficiency and capacity, 
air leaks must be stopped. 

In practice the importance of closing air leaks in the boiler setting is 
forcefully presented when patented devices for fuel saving are installed in 
boiler plants. Important economies in many cases are guaranteed if 
the new device is adopted, and then the claims of the agent are made 
good by instructing his workmen to go over the boiler, closing up all 
cracks in the setting through which cold air could enter, and at the same 
time covering the outside surface of the setting with a coating impervious 
to air. By such means the owner of the plant pays a high price for 
results that could have been obtained much more cheaply. 

The first of the principal objects of a boiler test stated above is to 
determine its capacity " rating." 1 The unit of capacity most generally 

1 When the steam supply is small or if, for any reason, the noise due to escaping 
steam from the calorimeters used is objectionable, a calorimeter may be shut off some- 
times between readings. The length of time the calorimeter is in operation must then 
be carefully noted in order to determine the weight of steam lost through it by cal- 

267 



268 



POWER PLANT TESTING 



used in steam boiler practice is the " boiler " horse power. Now this term 
horse power has two very distinct meanings in engineering practice. 
Usually it is taken to mean the rate of doing work or the work done in a 
definite period of time. In this sense it means, as in the case of engines, 
turbines, waterwheels, etc., 33,000 foot-pounds per minute. 1 In the 
case of a steam boiler, however, where the work done must be measured 
by the conversion of water into steam, a horse power is taken as the 
evaporation of 30 pounds of water at a temperature of 100 degrees 
Fahrenheit into steam at 70 pounds pressure above the . atmosphere. 
When this unit was adopted it was considered that 30 pounds per hour 
was approximately the requirement per indicated horse power of an 



m mmm wM 




Fig. 296. — Graphical Chart of a Boiler Trial. 

average engine. The Committee on Boiler Tests of the American Society 
of Mechanical Engineers have adopted what is in effect the same unit, 
stating it, however, somewhat differently — that a boiler horse power 
is equivalent to evaporating 34.5 pounds of steam per hour from feed- 
water temperature of 212 degrees Fahrenheit into steam at the same 
temperature. According to the latest steam tables this is equivalent 
to approximately 33,480 B.t.u. per hour, or 558 B.t.u. per minute. 

Unit of Evaporation. For reducing the results of the boiler tests to a 
common standard the term " unit of evaporation " is used. It is the 
heat required to evaporate a pound of water from and at 212 degrees 

culating the flow through its orifice (see page 189). The flow of steam, however, through 
the calorimeter must always be started before observations of the temperatures are to 
be taken in order to get constant conditions. 

1 This unit of horse power was adopted by James Watt, who considered it equiva- 
lent to the work done by a good London draft horse. 



BOILER TESTING 269 

Fahrenheit, 1 which according to standard steam tables is approximately- 
equivalent to 970.4 B.t.u. 2 

Graphical Log Sheets of boiler tests similar to the one shown in Fig. 296 
are very serviceable for checking the observations when made during the 
test as the data are taken. In the report of a test it shows also the 
relative irregularity or regularity of the conditions affecting the results. 

Standard Methods for Boiler Trials. The American Society of 
Mechanical Engineers has adopted rules for conducting boiler trials 
which are generally accepted in America and are also considered with 
favor in England. 3 These rules are so complete that they will be given 
here with practically no abridgment. 4 

RULES FOR CONDUCTING EVAPORATIVE TESTS OF BOILERS 
A.S.M.E. CODE OF 1912 

(general Procedure. Determine the object, take the dimensions, note 
the physical conditions, examine for leakages, install the testing appliance, 
etc., as pointed out in the general instructions given on pages 258 to 266, 
and make preparations for the test accordingly. 

Fuel. Determine the character of fuel to be used. 5 For tests of 
maximum efficiency or capacity of the boiler to compare with other 
boilers, the coal should be of some kind which is commercially regarded 
as a standard for the locality where the test is made. 

In the Eastern States the standards thus regarded for semi-bituminous coals are 
Pocahontas (Va. and W. Va.) and New River (W. Va.); for anthracite coals 
those of the No. 1 buckwheat size, fresh-mined, containing not over 13 per cent 
ash by analysis; and for bituminous coals, Youghiogheny and Pittsburg coals. 
In some sections east of the Allegheny Mountains the semi-bituminous Clear- 
field (Pa.) and Cumberland (Md.) are also considered as standards. These 
coals when of good quality possess the essentials of excellence, adaptability to 
various kinds of furnaces, grates, boilers, and methods of firing required, be- 
sides being widely distributed and generally accessible in the Eastern market. 

There are no special grades of coal mined in the Western States which are 
widely and generally considered as standards for testing purposes; the best coal 
obtainable in any particular locality being regarded as the standard of compari- 
son. 

A coal selected for maximum efficiency and capacity tests should be 
the best of its class, and especially free from slagging and unusual clinker- 
forming impurities. 

1 See also Equivalent Evaporation defined in same units, page 275. 

2 Marks and Davis' Steam Tables and Diagrams, see also Peabody's Steam Tables. 

3 Engines and Boilers by W. W. F. Pullen, pages 466-475. 

4 Journal of American Society of Mechanical Engineers, vol. 34, pages 1693-1872. 

5 This code relates primarily to tests made with coal. For reference to oil and gas 
fuel tests see page 276. 



270 



POWER PLANT TESTING 



The size of the coal, especially where it is of the anthracite class, 
should be determined by screening a suitable sample. 

Screens for Sizing Coal. The dimensions of screen openings to be used for sizing 
anthracite coals are given in the following table, the sizes in each case being 
the opening through which the specified grade will pass, and that over which it 
will be carried without passing through. The openings referred to are circular. 



ANTHRACITE COAL SIZES 



Name. 


Diameter of Opening 

through or over which 

Coal will pass, ins. 


Name. 


Diameter of Opening 

through or over which 

Coal will pass, ins. 




Through. 


Over. 


Through. 


Over. 




4§ 

If 

1 


3j 
2^ 

If 
f 
T5 


No. 1 Buckwheat 

No. 2 Buckwheat 

No. 3 Buckwheat 

Culm 


9 
16 

A 

s 

1 6 
3 
32 


A 

* 




Stove 




Pea 





The sizes and grades of bituminous and semi-bituminous coals vary so much 
according to kind and locality that there are no standards of size for these coals 
which are generally recognized. 

Bituminous coals in the Eastern States may be graded and sized as 
follows : 

(a) Run of mine coal; the unscreened coal taken from the mine. 

(b) Lump coal; that which passes over a bar-screen with openings 1| in. wide. 

(c) Nut coal; that which passes through a bar-screen with 1^-in. openings and 

over one with f-in. openings. 

(d) Slack coal; that which passes through a bar-screen with f-in. openings. 

Bituminous coals in the Western States may be graded and sized as 
follows: 

(a) Run of mine coal; the unscreened coal taken from the mine. 

(b) Lump coal; divided into 6-in., 3-in. and lj-in. lump, according to the diameter 

of the circular openings over which the respective grades pass; also 6 by 3 lump 
and 3 by 1| lump, according as the coal passes through a circular opening hav- 
ing the diameter of the larger figure and over that of the smaller diameter. 

(c) Nut coal; divided into 3-in. steam nut, which passes through an opening 3-in. 

diameter and over lj-in. diameter opening; lj-in. nut, which passes through 
a lf-in. diameter opening and over a f-in. diameter opening; f-in. nut, which 
passes through a f-in. diameter opening and over a f-in. diameter opening. 

(d) Screenings; that which passes through a lj-in. diameter opening. 



Apparatus and Instruments. 

for boiler tests are: 



The apparatus and instruments required 



(a) Platform scales for weighing coal and ashes. 
(6) Graduated scales attached to the water glasses. 



BOILER TESTING 271 

(c) Tanks and platform scales for weighing water (or water meters calibrated in 

place). 

(d) Pressure gages, thermometers, and draft gages. 

(e) Calorimeters for determining the calorific value of fuel and the quality of steam. 
(J) Furnace pyrometers. 

(g) Gas analyzing apparatus. 

Full directions regarding the use and calibration of the above-men- 
tioned appliances are given in the preceding chapters. 

Location of Instruments, (a) The feedwater thermometer should be placed in a 
thermometer well inserted in the feed pipe. Except in cases where an injector is 
used 1 the point selected should be as near as practicable to the boiler. Where an in- 
jector is employed, and the water is weighed or measured before it is supplied thereto, 
the well should be placed on the suction side of the injector, and the injector should 
receive steam through a short covered pipe connected directly to the boiler under test. 
If the steam is taken from some other source and it is of different pressure and different 
quality from that of the boiler under test, correction should be made for such differ- 
ence, and especially for any excessive moisture thus introduced into the feedwater. 
When the temperature of the water changes between the injector and boiler, as by 
the use of a heater or by excessive radiation, the temperature at which the water not 
only enters and leaves the injector, but that also at which it enters the boiler, should 
also be taken. In that case, the weight to be used is that of the water leaving the in- 
jector, computed from the heat units if not directly measured and the temperature, 
that of the water entering the boiler. The weight of condensed steam to be added to 
the weight of water entering the injector, to obtain that leaving the injector, may be 
computed by multiplying the weight entering by the proportion 



h-i — h 3 ' 
in which 

hi = heat units per pound of water entering injector. 
h 2 = heat units per pound of steam entering injector. 
h s = heat units per pound of water leaving injector. 

(b) The location of the steam calorimeter and steam thermometer should be as close 
to the boiler as possible. 

(c) Draft gages should be attached to each boiler between the hand damper and 
the boiler, and as near the damper as practicable. In the case of a plant containing a 
number of boilers, a gage should also be attached to the main flue between the regu- 
lating damper and the boiler plant. It is desirable also to have gages connected to 
the furnace or furnaces of the boilers, and in cases of forced blast, to the ashpits and 
blower ducts. If there is an economizer in the flue a gage should be connected to the 
flue at each end of this apparatus. The same draft gage may be used for all the points. 

1 In feeding a boiler undergoing test with an injector taking steam from another 
boiler, or from the main steam pipe from several boilers, the evaporative results may 
be modified by a difference in the quality of the steam from such source compared with 
that supplied by the boiler being tested, and in some cases the connection to the in- 
jector may act as a drip for the main steam pipe. If it is known that the steam from 
the main pipe is of the same pressure and quality as that furnished by the boiler under- 
going the test, the steam may be taken from such main pipe. 



272 POWER PLANT TESTING 

noted, provided suitable pipes are run from the gage to each, arranged so as to be readily 
connected to any of these points at will. 

(d) The flue thermometer should be located where it will show the average tem- 
perature of the whole body of gas. For an extremely large flue the thermometer may 
be placed in an oil pot of small diameter, which is suspended in the flue, and the ther- 
mometer lifted partially out of the oil when the temperature is read. 

(e) Samples for flue gas analysis should be drawn from the region near the center 
of the main body of escaping gases, and the point selected should be one where there is 
no chance for air leakage into the flue, which could affect the average quality. In a 
round or square flue having an area of not more than one-eighth of the grate surface, 
the sampling pipe may be introduced horizontally at a central point, or preferably a 
little higher than the central point, and the pipe should contain perforations extending 
the whole length of the part immersed and pointing toward the current of gas, the 
collective area of the perforations being less than the area of the pipe. 

Duration. The duration of tests to determine the efficiency of a hand- 
fired boiler, should be 10 hours of continuous running, or such time as 
may be required to burn a total of 250 pounds of coal per square foot of 
grate. 

In the case of a boiler using a mechanical stoker, the duration, where 
practicable, should be at least 24 hours. If the. stoker is of a type that 
permits the quantity and condition of the fuel bed at beginning and end 
of the test to be accurately estimated, the duration may be reduced to 
10 hours, or such time as may be required to burn the above noted total 
of 250 pounds per square foot. 

In commercial tests where the service requires continuous operation night and day, 
with frequent shifts of firemen, the duration of the test, whether the boilers are 
hand-fired or stoker-fired, should be at least 24 hours. Likewise in commercial 
tests, either of a single boiler or of a plant of several boilers, which operate regu- 
larly a certain number of hours and during the balance of the day the fires are 
banked, the duration should not be less than 24 hours. 

The duration of tests to determine the maximum evaporative capacity of a 
boiler, without determining the efficiency, should not be less than three hours. 

Starting and Stopping. The conditions regarding the temperature of 
the furnace and boiler, the quantity and quality of the live coal and ash 
on the grates, the water level, and the steam pressure, should be as nearly 
as possible the same at the end as at the beginning of the test. 

To secure the desired equality of conditions with hand-fired boilers, 
the following method should be employed: 

The furnace being well heated by a preliminary run, burn the fire low, and thor- 
oughly clean it, leaving enough live coal spread evenly over the grate (say from 
two to four inches) 1 to serve as a foundation for the new fire. Note quickly (1) 
the thickness of the coal bed as nearly as it can be estimated or measured; also 

1 1 to 2 inches for small anthracite coals. 



BOILER TESTING 273 

(2) the water level, 1 (3) the steam pressure, and (4) the time, and record the 
latter as the starting time. (5) Fresh coal should then be fired from that weighed 
for the test, (6) the ashpit should be thoroughly cleaned, and the regular work 
of the test proceeded with. 

Before the end of the test the fire should again be burned low and cleaned in 
such a manner as to (1) leave the same amount of live coal on the grate as at 
the start. When this condition is reached, observe quickly (2) the water level, 1 

(3) the steam pressure, and (4) the time, and record the latter as the stopping 
time. If the water level is not the same as at the beginning (5) a correction 

. should be made by computation, rather than by feeding additional water after 
the final readings are taken. Finally (6) remove the ashes and refuse from the 
ashpit. 

In a plant containing several boilers where it is not practicable to clean them 
simultaneously, the fires should be cleaned one after the other as rapidly as may 
be, and each one after cleaning charged with enough coal to maintain a thin 
fire in good working condition. After the last fire is cleaned and in working con- 
dition, burn all the fires low (say 4 to 6 in.), note quickly the thickness of each, 
also the water levels, steam pressure, and time, which last is taken as the start- 
ing time. Likewise when the time arrives for closing the test, the fires should 
be quickly cleaned one by one, and when this work is completed they should 
all be burned low the same as at the start, and the various observations made 
as noted. 

In the case of a large boiler having several furnace doors requiring the fire to 
be cleaned in sections one after the other, the above directions pertaining to 
starting and stopping in a plant of several boilers may be followed. 

To obtain the desired equality of conditions of the fire when a mechani- 
cal stoker other] than a chain grate is used, the procedure should be 
modified where practicable as follows: 

Regulate the coal feed so as to burn the fire to the low condition required for clean- 
ing. Shut off the coal-feeding mechanism and fill the hoppers level full. Clean 
the ash or dump plate, note quickly the depth and condition of the coal on the 
grate, the water level, 1 the steam pressure, and the time, and record the latter 
as the starting time. Then start the coal-feeding mechanism, clean the ashpit, 
and proceed with the regular work of the test. 

When the time arrives for the close of the test, shut off the coal-feeding mecha- 
nism, fill the hoppers and burn the fire to the same low point as at the beginning. 
When this condition is reached, note the water level, the steam pressure, and 
the time, and record the latter as the stopping time. Finally clean the ash plate 
and remove the ashes. 

In the case of chain grate stokers, the desired operating conditions should be 
maintained for half an hour before starting a test and for a like period before 
its close, the height of the throat plate and the speed of the grate being the 
same during both of these periods. 

The coal should be weighed and delivered to the firemen in portions sufficient for 
one hour's run, thereby ascertaining the degree of uniformity of firing. An 
ample supply of coal should be maintained at all times, but the quantity on 

1 Do not blow the water-glass column for at least one hour before these readings 
are taken. An erroneous indication may otherwise be caused by a change of tempera- 
ture and density of the water within the column and connecting pipe. 



274 POWER PLANT TESTING 

the floor at the end of each hour should be as small as practicable, so that the 
same may be readily estimated and deducted from the total weight. 

The records should be such as to ascertain also the consumption of feedwater 
each hour, and thereby determine the degree of uniformity of evaporation. 

Ashes and Refuse. The ashes and refuse withdrawn from the furnace 
and ashpit during the progress of the test and at its close should be 
weighed so far as possible in a dry state. If wet the amount of moisture 
should be ascertained and allowed for, a sample being taken and dried 
for this purpose. This sample may serve also for analysis and the deter- 
mination of unburned carbon and fusing temperature. 

Analyses of Flue Gases. For approximate determinations of the com- 
position of the flue gases, a portable type of apparatus should be em- 
ployed. If momentary samples are obtained the analyses should be 
made as frequently as possible, say every 15 to 30 minutes, depending 
on the skill of the operator, noting at the time the sample is drawn the 
furnace and firing conditions. If the sample drawn is a continuous one, 
the intervals may be made longer. 

Smoke Observations. In tests of bituminous coals requiring a deter- 
mination of the amount of smoke produced, observations should be made 
regularly throughout the trial at intervals of five minutes (or if neces- 
sary every minute), noting at the same time the furnace and firing 
conditions. 

Calculation of Results. The methods to be followed in expressing and 
calculating those results which are not self-evident are explained as 
follows : 

(a) Efficiency. The "efficiency of boiler, furnace and grate " is the relation be- 
tween the heat absorbed per pound of coal fired, and the calorific value of one 
pound of coal. 

The "efficiency of boiler and furnace" is the relation between the heat ab- 
sorbed per pound of combustible burned, and the calorific value of one pound 
of combustible. This expression of efficiency furnishes a means for comparing 
one boiler and furnace with another, when the losses of unburned coal due 
to grates, cleanings, etc., are eliminated. 

The " combustible burned" is determined by subtracting from the weight 
of coal supplied to the boiler, the moisture in the coal, the weight of ash and un- 
burned coal withdrawn from the furnace and ashpit, and the weight of dust, 
soot, and refuse, if any, withdrawn from the tubes, flues, and combustion cham- 
bers, including ash carried away in the gases, if any, determined from the analyses 
of coal and ash. The " combustible " used for determining the calorific value 
is the weight of coal less the moisture and ash found by analysis. 

The " heat absorbed " per pound of coal, or combustible is calculated by 
multiplying the equivalent evaporation from and at 212 degrees per pound of 
coal or combustible by 970.4. 

(b) Corrections for Moisture in Steam. When the percentage is less than 2 per cent 

it is sufficient merely to deduct the percentage from the weight of water fed. If 



BOILER TESTING 275 

the percentage is greater than 2 per cent or if extreme accuracy is required, the 
factor of correction equals 

X + P^4 (85) 

(H - q 2 ) 

in which X is the quality of the steam (one minus the decimal representing the 
percentage of moisture), P the proportion of moisture, 1 qi the total heat of water 
at the temperature of the steam, q 2 the total heat of the feed water, and H the 
total heat of saturated steam of the given temperature. 

(c) Correction for live steam, if any, used for aiding Combustion. If live steam is 

admitted into the furnace or ashpit for producing blast, injecting fuel, or aid- 
ing combustion, it is to be deducted from the total evaporation, and the net 
evaporation used in the various calculations. 

(d) Equivalent Evaporation. The equivalent evaporation from and at 212 deg. is 
obtained by multiplying the weight of water evaporated, corrected for moisture 
in steam, by the "factor of evaporation." The latter equals 

H-g 2 
970.4 ' 
in which H and q 2 are respectively the total heat of saturated steam and of the 
feedwater entering the boiler. When the steam is superheated, the total heat 
of the steam is that of saturated steam plus the product of the number of degrees 
of superheating by the specific heat of the steam. 

Unless otherwise provided, a combined boiler and superheater should be 
treated as one unit, and the equivalent of the work done by the superheater 
should be included in the evaporative work of the boiler. 

(e) Heat Balance. The " heat balance," or approximate distribution of the calorific 
value of the coal or combustible among the several items of heat utilized and 
heat lost, should be obtained in cases where the flue gases have been analyzed 
and a complete analysis made of the coal. 

The loss due to moisture in the coal is found by multiplying the difference 
between the total heat of one pound of superheated steam at the temperature 
of the escaping gases and the temperature of the air in the boiler room, by the 
weight of moisture in a pound of coal. 

The loss due to moisture formed by the burning of hydrogen is obtained by 
multiplying the total heat of one pound of superheated steam at the temper- 
ature of the escaping gases, calculated from the temperature of the air in the 
boiler room, by the proportion of the hydrogen, determined from the analysis 
of the coal, and multiplying the result by 9. 

The loss due to heat carried away in the dry gases is found by multiplying 
the weight of gas per pound of coal or combustible by the elevation of tem- 
perature of the gases above the temperature of the boiler room, and by the 
specific heat of the gases (0.24). The weight of gas referred to is obtained by 
finding the weight of dry gas per pound of carbon burned, using the formula 
11CQ 2 +8Q+7(C0+N) /Q ^ 

3 ( C0 2 + CO) ' (86) ' PagG 281 ' 

in which C0 2 , CO, O, and N are expressed in percentages by volume, and mul- 
tiplying this result by the proportion borne by the carbon burned to the whole 
amount of coal or combustible as determined from the results of the analysis 
of the coal, asli and refuse. 

1 Proportion of moisture is the ratio of the percentage of moisture in the steam 
to 100. 



276 POWER PLANT TESTING 

The loss due to incomplete combustion of carbon is found by first obtaining 
the proportion borne by the carbon monoxide in the gases to the sum of the 
carbon monoxide and carbon dioxide, and then multiplying this proportion by 
the proportion of carbon in the coal or combustible, and finally multiplying the 
product by 10,150, which is the number of heat units generated by burning to 
carbon dioxide one pound of carbon contained in carbon monoxide. 

The loss due to combustible matter in the ash and refuse is found by multi- 
plying the proportion that this combustible bears to the whole amount of coal or 
combustible, by its calorific value per pound. For most purposes it is sufficient 
to assume the combustible to be 14,600 B.t.u. per pound, the same as that of 
carbon. 

The loss due to moisture in the air is determined by multiplying the weight 
of such moisture per pound of coal or combustible by the elevation of temper- 
ature of the flue gases above the temperature of the boiler room and by 0.47. 
The weight of moisture is found by multiplying the weight of air per pound of 
coal or combustible by the moisture in one pound of air determined from read- 
ings of the wet- and dry-bulb thermometer. 
(/) Total Heat of Combustion of Coal, by Analysis. The total heat of combustion 
may be computed from the results of the ultimate analysis by using the formula 



-9 



14,600 C + 62,000 H - - + 4000 S, (69), page 227, 



in which C, H, O, and S refer to the proportions of carbon, hydrogen, oxygen 
and sulphur, respectively. 
(g) Air for Combustion. The quantity of air used may be calculated by the formulae: 

, , • , , , ' h 3.032 N 

Pounds of air per pound of carbon = — — — , 

CO2 -\- CO 

in which N, CO2 and CO are the percentages of dry gas obtained by analysis, 

and 

Lbs. of air per lb. of coal = lbs. air per lb. C X per cent C in the coal. 

The ratio of the air supply to that theoretically required for complete com- 

. ■ . N 
bustion is ■ Compare with formulas on page 249. 

Tests with Oil and Gas Fuels. Tests of boilers using oil or gas for fuel 
should accord with the rules here given, excepting as they are varied to 
conform to the particular characteristics of the fuel. The duration in 
such cases may be reduced, and the " flying " method of starting and 
stopping employed. 

The table of data and results should contain items stating character of furnace and 
burner, quality and composition of oil or gas, temperature of oil, pressure of 
steam used for vaporizing and quantity of steam used for both vaporizing and 
for heating. 

TABLE 1. DATA AND RESULTS OF EVAPORATIVE TEST — SHORT FORM 
CODE OF 1912 

(1) Test of boiler located at 

to determine conducted by 

(2) Kind of furnace 

(3) Grate surface sq. ft. 



BOILER TESTING 277 

(4) Water-heating surface 1 sq. ft. 

(5) Superheat ing surface 1 sq. ft. 

(6) Date 

(7) Duration hrs. 

(8) Kind and size of coal '. 

Average Pressures, Temperatures, etc. 

(9) Steam pressure by gage lbs. per sq. in. 

(9a) Absolute steam pressure lbs. per sq. in. 

(10) Temperature of feedwater entering boiler deg. F. 

(11) Temperature of escaping gases leaving boiler deg. F. 

(12) Force of draft between damper and boiler ins. water 

(13) Percentage of moisture in steam, or number deg. of superheating (per cent or deg. F.) 

Total Quantities 

(14) Weight of coal as fired 2 lbs. 

(15) Percentage of moisture in coal per cent 

(16) Total weight of dry coal consumed lbs. 

(17) Total ash and refuse lbs. 

(18) Percentage of ash and refuse in dry coal per cent 

(19) Total weight of water fed to the boiler 3 lbs. 

(20) Total water evaporated, corrected for moisture in steam lbs. 

(21) Total equivalent evaporation from and at 212 deg. F lbs. 

Hourly Quantities and Rates 

(22) Dry coal consumed per hour lbs. 

(23) Dry coal per sq. ft. of grate surface per hour lbs. 

(24) Water evaporated per hour corrected for quality of steam lbs. 

(25) Equivalent evaporation per hour from and at 212 deg. F lbs. 

(26) Equivalent evaporation per hour from and at 212 deg. F. per sq. ft. of water- 

heating surface lbs. 

Capacity and Economy Results 

(27) Evaporation per hour from and at 212 deg. F. (same as Line 25) lbs. 

(28) Boiler horse power developed (Item 27 -r 34|) :.:,... .bl.h.p. 

(29) Rated capacity, in evaporation from and at 212 deg. F. per hour. ......... .lbs. 

(30) Rated boiler horse power bl.h.p. 

(31) Percentage of rated capacity developed. per cent 

(32) Water fed per lb. of coal fired (Item 19 + Item 14) . . lbs. 

(33) Water evaporated per lb. of dry coal (Item 20 -f- Item 16) ...:...... lbs. 

(34) Equivalent evaporation from and at 212 deg. F. per lb. of dry coal (Item 

21 -5- Item 16) .'. lbs. 

(35) Equivalent evaporation from and at 212 deg. F. per lb. of combustible [Item 

21 -=- (Item 16 - Item 17)] >.lf. - lbs. 

1 See page 258 for definition of heating surfaces. 

2 The term "as fired" means actual condition including moisture, corrected for 
estimated difference in weight of coal on the grate at beginning and end of test. 

3 Corrected for inequality of water level and steam pressure at beginning and end of 
test. 



278 POWER PLANT TESTING 



Efficiency 



(36) Calorific value of 1 lb. of dry coal B.t.u. 

(37) Calorific value of 1 lb. of combustible B.t.u. 

(38) Efficiency of boiler, furnace and grate 100 X — — = — per cent 

L Item 36 J 

f Item 35 X 970. 4~| 

(39) Efficiency of boiler and furnace 100 X per cent 

|_ Item 37 J 

Cost of Evaporation 

(40) Cost of coal per ton of ... . lbs. delivered in boiler room dollars 

(41) Cost of coal required for evaporating 1000 lbs. of water from and at 212 deg., dollars 

TABLE 2. DATA AND RESULTS OF EVAPORATIVE TEST — COMPLETE 
FORM, CODE OF 1912 

(1) Test of boiler located at 

to determine conducted by 



Dimensions, Proportions, etc. 

(2) Number and kind of boilers 

(3) Kind of furnace 

(4) Grate surface width length area sq. ft. 

(5) Approximate width of air spaces in grate ins. 

(6) Proportion of air space to whole grate surface . per cent 

(7) Water-heating surface sq. ft. 

(8) Superheating surface sq. ft. 

(9) Ratio of water-heating surface to grate surface , to 1 

(10) Ratio of minimum draft area to grate surface 1 to 

(11) Date 

(12) Duration hrs. 

(13) Kind of coal 

(14) Size of coal 

Average Pressures, Temperatures, Quality of Steam, etc. s 

(15) Steam pressure by gage lbs. per sq. in. 

(16) Barometric pressure ins. mercury = lbs. per sq. in. 

(16a) Absolute steam pressure lbs. per sq. in. 

(17) Force of draft at dampers of individual boilers ins. water 

(18) Force of draft in main flue near boilers ins. water 

(19) Force of draft in main flue between economizer and chimney ins. water 

(20) Force of draft in furnaces ins. water 

(21) Force of blast in ashpits ins. water 

(22) State of weather 

(23) Temperature of external air deg. F. 

(24) Temperature of fireroom deg. F. 

(25) Temperature of steam deg. F. 

(26) Normal temperature of saturated steam deg. F. 

(27) Temperature of feedwater entering flue heater or economizer deg. F. 

(28) Temperature of feedwater leaving heater or economizer and entering 

boilers deg. F, 



BOILER TESTING 279 

(29) Temperature of gases leaving boilers deg. F. 

(30) Temperature of gases leaving economizer deg. F. 

(31) Percentage of moisture in steam per cent 

(32) Number of degrees of superheating deg. F. 

(33) Quality of steam (dry steam = unity) 

Total Quantities 

(34) Weight of coal as fired 1 lbs. 

(35) Percentage of moisture in coal per cent 

(36) Total weight of dry coal consumed lbs. 

(37) Total ash and refuse lbs. 

(38) Total combustible consumed (Line 36 — Line 37) lbs. 

(39) Percentage of ash and refuse in dry coal per cent 

(40) Total weight of water fed to boiler 2 lbs. 

(41) Total water evaporated corrected for moisture in steam lbs. 

(42) Factor of evaporation, based on temperature of water entering boilers 

(43) Total equivalent evaporation from and at 212 deg. F. lbs. 

Hourly Quantities and Rates 

(44) Dry coal consumed per hour lbs. 

(45) Combustible consumed per hour lbs. 

(46) Dry coal per sq. ft. of grate surface per hour lbs. 

(47) Water evaporated per hour, corrected for quality of steam lbs. 

(48) Equivalent evaporation per hour from and at 212 deg. 3 F lbs. 

(49) Equivalent evaporation per hour and at 212 deg. F. per sq. ft. of water-heat- 

ing surface 2 lbs. 

Proximate Analysis op Coal 

(50) Fixed carbon per cent 

(51) Volatile matter per cent 

(52) Moisture per cent 

(53) Ash per cent 

100 per cent 

(54) Sulphur, separately determined . per cent 

Ultimate Analysis of Dry Coal 

(55) Carbon (C) per cent 

(56) Hydrogen (H) per cent 

(57) Oxygen (O) per cent 

(58) Nitrogen (N) per cent 

(59) Sulphur (S) per cent 

(60) Ash per cent 

100 per cent 

(61) Moisture in sample of coal as received per cent 

1 The term "as fired" means actual condition including moisture, corrected for 
difference in weight of coal on grate at beginning and end of test. 

2 Corrected for inequality of water level and steam pressure at beginning and end of 
test. 

3 The symbol U.E. meaning "units of evaporation" (see page 268) may be sub- 
stituted for the expression, equivalent water evaporated into dry steam from and at 
212 deg. Fahrenheit. 



280 POWER PLANT TESTING 



Analysis of Ash and Refuse 

(62) Carbon per cent 

(63) Earthy matter per cent 

(64) Temperature of fusion of ash deg. F. 

Calorific Value 

(65) Calorific value of 1 lb. of dry coal by calorimeter B.t.u. 

(66) Calorific value of 1 lb. of combustible by calorimeter B.t.u. 

(67) Calorific value of 1 lb. of dry coal by analysis B.t.u. 

(68) Calorific value of 1 lb. of combustible by analysis B.t.u. 

Capacity, Economy Results and Efficien'cy 

(69) Evaporation per hour from and at 212 deg. F. (same as Line 48) lbs. 

(70) Boiler horse power developed (Line 69 -5- 34|) bl.h.p. 

(71) Rated capacity per hour, from and at 212 deg. F lbs. 

(72) Rated boiler horse power bl.h.p. 

(73) Percentage of rated capacity developed per cent 

(74) Water fed per lb. of coal (Item 40 -^ Item 34) lbs. 

(75) Water evaporated per lb. of dry coal (Item 41 -r- Item 36) lbs. 

(76) Equivalent evaporation from and at 212 deg. F. per lb. of coal fired (Item 

43 -e- Item 34) lbs. 

(77) Equivalent evaporation from and at 212 deg. F. per lb. of dry coal (Item 

43 -v- Item 36) lbs. 

(78) Equivalent evaporation from and at 212 deg. F. per lb. of combustible (Item 

43 -v- Item 38) lbs. 



T Item 77 X 970.4] 

s 100 X ; per cent 

|_ Item 65 J 

(80) Efficiency of boiler and furnace 100 X — 

L Item 66 J 



(79) Efficiency of boiler, furnace, and grate 100 X 

Item di> J 

5 X 970.41 

.per cent 



Cost of Evaporation 

(81) Cost of coal per ton of .... lbs. delivered in boiler room dollars 

(82) Cost of coal required for evaporating 1000 lbs. of water under observed 

conditions dollars 

(83) Cost of coal required for evaporating 1000 lbs. of water from and at 212 

deg. F dollars 

Smoke Data 

(84) Percentage of smoke as observed per cent 

(85) Weight of soot per hour obtained from smoke meter 

Methods of Firing 

(86) Kind of firing, whether spreading, alternate, or coking 

(87) Average thickness of fire ins. 

(88) Average intervals between firings for each furnace during time when fires are 

in normal condition min. 

(89) Average interval between times of leveling or breaking up min. 



BOILER TESTING 



281 



Analysis of Dky Gases by Volume 

(90) Carbon dioxide (C0 2 ) per cent 

(91) Oxygen (O) per cent 

(92) Carbon monoxide (CO) per cent 

(93) Hydrogen and hydrocarbons per cent 

(94) Nitrogen, by difference (N) per cent 

100 per cent 

HEAT BALANCE BASED ON DRY COAL AND COMBUSTIBLE 





Dry Coal as Fired. 


Combustible 
Burned. 




B.t.u. 


Per Cent. 


B.t.u. 


Per Cent. 


(95) Heat absorbed by the boiler (Line 77 or 78 X 970.4) 

(96) Loss due to evaporation of moisture in coal (page 275) 

(97) Loss due to heat carried away by steam formed by the 


























(102) Loss due to unconsumed hydrogen and hydrocarbons, to 








(103) Total calorific value of 1 lb. of dry coal or combustible 




100 











COMPUTATION OF THE WEIGHT OF THE CHIMNEY GASES FROM THE 
ANALYSIS BY VOLUME OF THE DRY GAS 

Two methods of calculating from the analysis by volume of the dry 

chimney gases the number of pounds of dry chimney gases per pound 

of carbon, or the weight of air supplied per pound of carbon, have been 

given by different writers. These may be expressed in the shape of 

formulas as follows: 

1 1 CO, + 8 O + 7 (CO + N) 



(A) Pounds dry gasper pound C = 



(B) Pounds air per pound C 



= 5.1 



3 (C0 2 + CO) 
2(C0 2 + O) + CO 



(87) 



C0 2 + CO • ' " 
in which C0 2 , 2 , CO and N are percentages by volume of the gases. 

Formula A may be^derived from the method of computation given in 
Mr. R. S. Hale's paper on " Flue-Gas Analyses," Transactions American 
Society of Mechanical Engineers, vol. 18, page 902, and formula B from 
the method given in Peabody's and Miller's " Treatise on Steam Boilers." 
Both are based on the principle that the density, relatively to hydrogen, 
of an elementary gas (O and N) is proportional to its atomic weight, and 
that of a compound gas (CO and C0 2 ) to one-half its molecular weight. 
Both formulas are very nearly accurate when pure carbon is the fuel 
burned, but formula B is inaccurate when the fuel contains hydrogen, for 
the reason that the portion of the oxygen of the air supply which is re- 



282 



POWER PLANT TESTING 



quired to burn the hydrogen is contained in the chimney gas as water 
vapor and does not appear in the analysis of the dry gas. 

The following calculations of a supposed case of combustion of hydrog- 
enous fuel illustrates the accuracy of formula A and the inaccuracy of 
formula B. Assume that the coal has the following analysis: C, 66.50; 
H, 4.55; 0, 8.40; N, 1.00; water, 10.00; ash and sulphur, 9.55— total, 
100. Assume that one-tenth of the C is burned to CO, and nine-tenths 
to CO2; that the air supply is 20 per cent in excess of that required for 
this combustion; that the air contains 1 per cent by weight of moisture; 
and that the S in the coal may be considered as part of the ash. We then 
have the following summary of results of the combustion of 100 pounds of 
coal: 





from 
Air. 


N=OXI5- 


Total Air. 


C0 2 . 


CO. 


H 2 0. 


59.85 lbs. C toC0 2 X2f 


159.60 

8.87 

28.00 


534.31 

29.70 
93.74 


693.91 

38.57 
121.74 


219.45 






6.65 " CtoCOxH 
3.50 " HtoH 2 Ox8 


15.52 


3L50 




196.47 
39.29 


657.75 

"loo" 

131.55 


854.22 
170.84 




1.05 " H to H 2 ( 
8.40 " HtoHoOj 
10.00 " Water 
1.00 " N 






9.45 
10.00 


9.55 " Ash and S 








100.00 

Excess of air 20 per cent. 
















1025.06 




Moisture in air 1 per cent. 






10.25 


Total wt. gases, 1125.76 lbs.= 
Total dry gases, 1064.56 lbs. 

Per Cent 
Total dry gases, by weight, 
Total dry gases, by volume, 


39.29 


3.69 
3.508 


790.30 

N 
74.24 
80.656 




219.45 

C0 2 
20.61 
14.252 


15.52 

CO 
1.546 
1.584 


61.20 



Total gases 1125.76 + ash and S 9.55 = 1135.31 lbs. total products. 
Total air 1025.06 + moisture in air 10.25 + coal 100 = 1135.31 lbs. 
Dry gas per lb. coal 10.6456; per lb. carbon = 10.6456 -=- .665 = 16.008 
Dry air per lb. coal 10.2506; per lb. carbon = 10.2506 + .665 = 15.414 
Computation of the weight of dry gas and of air per lb. carbon. 



Formula A: 
Dry gas per lb. C = 
Formula B: 



14.252 X 11 + 3.508 X 8 + 82.240 X 7 



Air per pound C = 5.1 



3 (14.252 + 1.584) 
2 (14.252 + 3.508) + 1584 



= 16.008 pounds. 



13.589 pounds. 



14.252 + 1.584 
The error in the last result is 15.414 - 13.589 = 1.825 pounds. 

Professor D. S. Jacobus gives another formula for the air per pound 
of carbon, in which the error of formula 87 is almost entirely avoided. 



BOILER TESTING 283 

It is 

Formula C: 

Air per pound C = ^C^FCO) * °- 77 ' ° r 0.33 (C0 2 + 00) ' (88) 

in which N, C0 2 , and CO are the percentages by volume of these gases. 
Making the computation from the data of the above analysis, we have : 

Air per pound C = ^ ^^ 1.584) = 15 " 434 P ° Unds ' 
the true value being 15.414 pounds. 



CHAPTER XII 



STEAM ENGINE TESTING 

Most important of the tests made of nearly all classes of machinery is 
that for mechanical effic ency; meaning the comparison of the useful 
work performed with the amount of work theoretically possible to obtain 
with a perfect machine. In other words, in an engine the mechanical 
efficiency, E m , is the ratio of the brake horse power to the indicated 
horse power, or 

_ b.h.p. 
i.n.p. 

STEAM ENGINE TESTING 
TESTS FOR MECHANICAL EFFICIENCY AND FRICTION 
Test made by 



(89) 



Date 

Description of engine tested 



Tare of Brake lbs. Length of brake arm feet . 

Engine and Brake Constants (see pages 143 and 148) 



No. of 

Read- 


Time. 


Weight on 
Brake, lbs. 


R.P.M. 


Areas of 

Indicator, 

Cards, sq. ins. 


Indicated 
Horse Power. 


Brake 
Horse 
Power. 


Fric- 
tion 
Horse 
Power. 


Mech. 
Effic. 


ing. 


Gross. 


Net. 




Head 
End. 


Crank 
End. 


Head 
End. 


Crank 
End. 


Total. 































The difference between the indicated horse power and the brake 
horse power is called the friction horse power. In many cases with 
very large engines, it is not readily possible to obtain the brake horse 
power directly, and in such cases it is customary to obtain approxi- 
mately the horse power lost in friction from a so-called " friction indicator 
diagram," obtained from the areas of indicator diagrams when the only 
work done is that required to overcome its own friction, or in common 
parlance, when the engine is " running light." The brake horse power 
is then taken to be the difference between the indicated horse power 

284 



STEAM ENGINE TESTING 



285 



and the friction horse power. Such a determination of friction horse 
power and of mechanical efficiency by calculation cannot be considered 
very accurate, because the friction of an engine increases slightly with 
increasing loads. 

Observed and calculated data of mechanical efficiency may be tabu- 
lated as shown in table on page 284. 

Valve Setting (Slide Valve Engines). In order that steam may be 
used economically in an engine, it is necessary that the valve be set care- 
fully and accurately, so that when an indicator card is taken the diagram 
obtained will be as nearly as possible like the ideal. Adjustment of a 
slide valve on an engine is accomplished in two different ways, with differ- 
ent effects: 

(1) By moving the valve on its stem; 

(2) By adjusting the eccentric. 

Typical slide valves are shown in Figs. 297 and 298. 



Exhaust Lap _^f L*. 
I ' 



-=* ^ Exhaust Lap 



Steam Lap 




J Exhaust Port 
Ordinary D-slide Valve in Mid-position. 



f 



s 

4 ■ 



Exhaust LapjwJ 



Steam Lap 



H Exhaust Lap 




Fig. 298. — Piston Type of Slide Valve in Mid-position. 

To Set the Valve for Equal Leads. The first step in setting a valve 
is to place the engine on dead-center and adjust the angle between the 
crank and eccentric so that the valve opens the port leading to the 
cylinder a slight amount. The width of the opening should be measured 
and recorded as a preliminary value of the lead on that end, 1 — suppose 

1 It is assumed of course that corresponding dimensions of the ports are the same 
at the two ends of the valve seat. 



286 POWER PLANT TESTING 

for example it is | inch. Then the engine should be placed on the 
opposite dead-center and the port opening on that end measured and 
recorded as the preliminary value of the lead on that end, suppose it 
is T V inch. There is then a difference in lead on the two ends of T V inch. 
The valve must be moved on its stem a distance equal to half the 
difference, or -^ inch. This movement of the valve will be in a direction 
away from the port having the smaller opening. 

By the method described the two leads of the valve will be made the 
same; in other words, the distance the valve uncovers the steam ports 
when the engine is on the dead-center will be the same at both ends of the 
cylinder. But while the leads are equal they are not necessarily the 
required amount and it remains to set the eccentric to give the leads de- 
sired. Place the engine once more accurately on dead-center 1 and after 
loosening the eccentric move it on the shaft so as to change the lead to 
the amount desired. As a final check, after securing the eccentric, the 
engine can be placed on the other dead-center to see that the lead is 
correct. 2 

To set the valve for equal cut-offs, the valve is first set on its stem so 
that the travel will be the same on both sides of the mid-position as 
explained at the bottom of this page to make its movement symmetrical 
with the ports. Now an adjustment of the eccentric must be made 
so that steam will be cut off at each end of the cylinder when the piston 
has moved the same distances or the same per cent of the stroke from 
the two ends. To perform this adjustment mark on the cross-head as 
accurately as possible the limits of the stroke, and set the cross-head at 
the per cent of the stroke for cut-off appearing to be most suitable for 
the conditions of load. Move the eccentric on the shaft in the direction 

1 An engine can be put on dead-center quite accurately by the " method of tram- 
mels." When the engine is just a little off the center to be determined, make small 
scratch-marks opposite each other both on the cross-head and on one of the guides. 
Now set a pair of dividers or trammels with one end resting on the bedplate of the en- 
gine, its foundation, or some convenient stationary object near the fly-wheel, and with 
the other end mark a point on the fly-wheel. The engine should then be moved over 
or beyond the dead-center until the marks made on the cross-head and on the guide 
come together again. With the dividers set with the points the same distance apart 
as before again put a mark on the fly-wheel. Then if the engine is turned back so that 
the end of the dividers used to mark on the fly-wheel is at a point half way between 
the two marks, it will be set quite accurately on the dead-center required. In all these 
adjustments care must be taken to turn the engine each time in the same direction 
with respect to the dead-center so that the lost motion or back lash is taken up in the 
same direction. The engine must be placed accurately on center because when the 
crank is near the dead-center the eccentric is in such a position that a slight movement 
of the shaft causes considerable movement of the valve. 

2 This method applies only explicitly to a valve like the one in Fig. 297, which takes 
steam on the " outside." When the valve takes steam on the inside (Fig. 298) the 
eccentric must be moved in the opposite direction. 



STEAM ENGINE TESTING 287 

in which the engine is to run until it can be seen that the valve would be 
just closing the steam port at the end of the cylinder from which the 
piston is moving. Fasten the eccentric securely in this position and 
turn the engine over to observe whether the valve will be just closing the 
other steam port when the piston has moved the same distance, measured 
on the cross-head, from the other end of the cylinder. If the setting is 
not correct, the error should be halved, correcting for one half the error 
by moving the valve on the stem and for the other half by moving the 
eccentric on the shaft. This operation, which is a " cut and try" 
process, must be repeated until the required setting is secured. 

Methods similar to those described are preferred usually for the accu- 
rate setting of the slide valves of slow- and medium-speed engines. 
High-speed engines as well as slow-speed engines of the Corliss type 
have their valves set usually on the basis of the information secured 



Cut Off 




Compression 



Atmospheric Line 
Fig. 299. — Indicator Diagram Illustrating the Point of Cut-off. 

from indicator diagrams taken on the engines, showing approximately the 
" timing " of the events of the stroke. To set a slide valve successfully 
by the " indicator " method, the valve and ports should be measured 
to determine the " lap " dimensions and port openings indicated in 
Fig. 297 page 285, as well as the valve travel. With these data a 
Zeuner 1 valve diagram should be constructed, showing a good steam 
distribution for assumed lead or cut-off. Then construct the theoretical 
indicator card from the Zeuner diagram and adjust the setting of the 
valve on the stem and the eccentric on the shaft until a close approxi- 
mation to the theoretical card is obtained. In this adjustment the first 
thing to be done is to equalize the travel of the valve by locating it 
on its stem so that the travel will be the same on both sides of its mid- 
position. 

Use a spring in the indicator light enough to give a diagram about 1£ 

1 It is beyond the scope of this book to take up a discussion of valve diagrams. 
The theory and construction of the Zeuner diagram are given in nearly all books on the 
steam engine. Bilgram valve diagrams, although excellent for designers, are not as 
good as the Zeuner diagram for valve setting requirements. 



288 POWER PLANT TESTING 

inches high so that events of the stroke, — admission, cut-off, release, and 
compression, will be shown as clearly as possible. Sometimes it is difficult 
to determine these events on a diagram on account of the curves gradually 
running into each other without the point separating the different curves 
being clearly defined. A good method for such cases is to produce along 
their regular trend both of the curves of which the intersection is re- 
quired and take for the intersection the point where these curves cross 
each other. The method is illustrated on an indicator card in Fig. 299 
showing the point of cut-off. 

In a slide-valve engine it is not possible to set the valve to secure at the 
same time equal cut-offs and equal leads. 

Ideal and imperfect indicator diagrams taken from slide-valve and 
Corliss engines are shown in Fig. 300. A little study of such diagrams 
may help to solve many difficulties in valve setting. 

Setting Corliss Valves. A brief description 1 of the essential parts of 
the valve gear of a Corliss engine will assist in obtaining a clearer con- 
ception of the subject. In Figs. 301 and 302 similar letters of refer- 
ence indicate the same parts of the mechanism. 

Fig. 301 shows all the essential parts of the valve gear. The steam 
valves work in the chambers S, S and the exhaust valves work in the 
chambers E, E. The double-armed levers AC, AC work loosely on the 
hubs of the valve-stem brackets and the lever arms B, B ; the former are 
connected to the wrist plate W by the rods M, M; the levers B, B are 
keyed to the valve stems V, V, and are also connected by the rods O, O 
to the dashpots D, D. The double-armed levers carry at their outer 
ends C, C hardened steel catch plates, which engage with arms B, B, 
making the two arms B and C work in unison until steam is to be cut off; 
at this point another set of levers H, H, connected by the cam rods G, G 
to the governor, come into play, causing the catch plates to release the 
arms B, B, the outer ends of which are then pulled downward by the 
weight of the dashpot plunger, causing the steam valves to rotate on their 
axes and thus cut off steam. These are the essential features of the 
Corliss gear, although the design of the mechanism is greatly modified by 
different builders. 

The exhaust valve arms F are connected to the wrist plate by the rods 
N, N, and it is seen that all the valves receive their motion from the wrist 
plate; the latter receives its motion from the hook rod I; this rod is 
generally attached to a rocker arm, not shown; to this arm the eccentric 
rod is also attached. The carrier arm is usually placed about midway 
between the wrist plate and eccentric, and in the center of its travel 
stands in a vertical position. 

1 This description is mainly from American Machinist, vol. 18, page 391. For clear- 
ness the article is considered unusually good. 



STEAM ENGINE TESTING 



289 




290 



POWER PLANT TESTING 



The setting of the valves is not a difficult matter when, on the wrist 
plate, its support, valves and cylinder, the customary marks have been 
placed for finding the relative positions of wrist plate and valves. 

Now referring to Fig. 302, when the back bonnets of the valve chambers 
have been taken off, there will be found a mark or line a on the end of each 
valve s, s, coinciding with the working or opening edges of each valve; 
another line b will be found on each face of the steam valve chamber coin- 
ciding with the working edge of the valve, and the line h, on the face of 
each exhaust valve chamber, coincides with the working edge of the 




Fig. 301. — Corliss Valve Gear. 



exhaust port. On the hub of the wrist plate will be found a line d, 
coinciding with the center line d, k; lastly, there are three lines f, c, f, on 
the hub of the wrist-plate support, placed in such a way that when the 
line d coincides with the line c, the wrist plate will stand exactly in the 
center of its motion, and when the line d coincides with either of the lines 
f, f, the wrist plate will be at one of the extreme ends u or v of its travel. 
It should be noticed that since the lines f , e, f are drawn on the periphery 
of the hub of the wrist-plate support, and the line d is drawn on the periph- 
ery of the wrist-plate hub, these lines cannot stand in a vertical line, 
as shown. This way of showing them has been adopted simply for the 
purpose of making the matter plain. 

In setting the valves the first step will be to set the wrist plate in its 



STEAM ENGINE TESTING 



291 



central position, so that lines c and d will coincide, and fasten the wrist 
plate in this position by placing a piece of paper between it and the 
washer L on its supporting pin. Now set the steam valves so that they 
will have a slight amount of lap, that is to say, the lines a, a must have 
moved a little beyond the lines b, b ; the amount of this lap depends much 
on individual preference and experience; it ranges from T V to \ inch for 
small engines, and from \ to T %- inch for comparatively large engines. 
This lap is obtained by lengthening or shortening the rods M, M by means 
of the adjusting nuts. 

Now by lengthening or shortening the rods N, N and by moving the 
adjusting nuts, place the exhaust valves e, e, in a position so that the 
working edges will just open the exhaust ports, or, in other words, place 
the lines g and h nearly in line with each other. Some engineers prefer 
a slight amount of lap, others prefer a slight opening of the exhaust ports 




Fig. 302. — Diagram of a Corliss Valve Mechanism. 

when the valves are in this position; under these conditions the lines 
g and h cannot be in line, but will stand apart, as indicated in the 
diagram. The distance between these lines will, of course, be equal to 
the desired amount of opening. For small engines it is about T V inch, 
and for larger engines may be increased to T 3 g inch, but in any case the 
amount of this opening should be less than the lap of the steam valves, 
otherwise there will be danger of steam blowing through without 
doing work. 

The paper between the wrist plate and the washer on the supporting 
pin should now be taken out, so that the wrist plate connected to the 
valves can be swung on its pin. 

The next step will be to give some attention to the rocker arm. Set 
this arm in a vertical position by means of a plumb-line, and connect the 
eccentric rod to it, then turn the eccentric around on the shaft, and see 
that the extreme points of travel are at equal distances from the plumb- 
line. To secure this a little adjustment in the stub end of the eccentric 



292 POWER PLANT TESTING 

rod may be necessary. Now connect the hook rod I to its pin on the 
wrist plate, and again turn the eccentric around on the shaft, and thus 
determine the extreme points of travel of the wrist plate. If all parts 
have been correctly adjusted, the line d will coincide with the lines f, f 
at the extreme points of travel; if this is not the case, the hook rod will 
have to be adjusted at its stub end so as to obtain the desired eqaalized 
motion of the wrist plate. 

The next step will be to set the valves correctly with respect to the 
position of the crank. To do so the lengths of the rods M, M, N and 
N must not be changed, but the following procedure should be followed : 
Place the crank on one of its dead-centers, and turn the eccentric loosely 
on the shaft in the direction in which the engine is to run, until the steam 
valve nearest to the piston shows an opening or lead of £% to § inch, 
according to size of engine, the smaller lead, of course, being adopted for 
small engines. After the proper lead has been given to this valve, secure 
the eccentric, and turn the shaft with eccentric in the same direction in 
which the engine is to run until the crank is on the opposite dead-center, 
and notice if the opening or lead at this end of the cylinder is the same 
as on the other steam valve; if not, shorten or lengthen slightly, as may 
be necessary, the connection between wrist plate and eccentric. Much 
adjustment in the length of these connections is not permissible without 
resetting the valves with reference to the wrist plate. 

The only thing which now remains to be done is to adjust the cam rods, 
G, G. To do this, secure the governor balls in their highest position, and 
disconnect the hook rod from wrist pin. Lengthen or shorten the cam 
rods G, G, so as to bring the detachment apparatus into action, swing the 
wrist plate back and forward and make such adjustments in the rods G, G, 
as to permit the steam valves to be released when the steam port has been 
opened about | inch. This adjustment is for the purpose of keeping the 
engine under the control of the governor, in case, for some reason or 
another, the load on the engine is suddenly thrown off. After this adjust- 
ment the governor balls should be placed in their lowest position, in 
which the releasing gear should not detach the steam valves, but allow 
the steam to follow nearly full stroke. Sometimes the releasing gear is 
constructed in such a manner as to close the steam valves automatically, 
in case the belt leading to the governor should be broken, or the load on 
the engine suddenly thrown off. In cases of this kind the governor balls 
need not be placed in their highest position, but should be placed in their 
lowest position, and the wrist plate moved to either end of its extreme 
travel. The steam port opposite this end of travel of wrist plate will then 
be wide open. Now adjust the corresponding cam rod so that the releasing 
gear is nearly on the point of releasing the valve; then move the wrist 
plate to other end of its extreme travel, and adjust the other cam rod in 



STEAM ENGINE TESTING 293 

the same manner. To prove the correctness of the cut-off adjustment, 
raise the governor balls to about a position where they would be when at 
work, or to a medium height, and block them there; then, with the con- 
nection made between the eccentric and the wrist plate, turn the engine 
shaft slowly in the direction in which it is to run, and when the valve is 
released measure upon the slide the distance through which the cross- 
head has moved from its extreme position. Continue to turn the shaft 
in the same direction, and when the other valve is released, measure the 
distance through which the cross-head has moved from its extreme 
position, and if the cut-off is equalized, these two distances will be equal 
to each other. If they are not, adjust the length of the cam rods until 
the points of cut-off are at equal distances from the beginning of the 
stroke. Replace the back bonnets and see that all connections have been 
properly made, which will complete the setting of the valves. Wherever 
convenient, it is desirable that an indicator be applied to the engine 
when at work, and the setting of the valves tested. If necessary, they 
should be readjusted for the best possible condition for economical work. 

Clearance Determination of an Engine. This test is made usually to 
determine the clearance volume of a steam or a gas engine. It is some- 
times important to know the clearance volume of an engine, as it materi- 
ally affects the expansion curve of the engine. If it is too large it causes 
an excessive loss in the engine. The clearance volume is also necessary 
if a theoretical expansion curve is to be constructed. 

The engine is first set on dead-center with the piston at the head end 
of the cylinder. This is done by the " method of trammels " (see foot- 
note, page 286) . Then the steam chest cover and valve are to be removed 
and a rubber gasket under a block of wood is placed over both steam-port 
openings in the valve seat and bolted on. Usually candle wicking must 
be packed around the piston to stop excessive leakage. For this purpose 
the cylinder head must be removed and again replaced. 

Two vessels filled with clean water should be provided and weighed. 
The clearance space is to be filled from one vessel, the time required being 
taken. As soon as the space is filled the first vessel is removed and the 
space is kept filled with water from the other vessel for five minutes. 
The vessels are then again weighed and the water used from each of them 
determined. The average rate of leakage while filling the space is 
usually assumed to be one-half the rate of leakage when full of water as 
during the leakage test. 

If W\ = weight in pounds to fill the clearance space; t minutes = the 
time required to fill the clearance space; and w 2 = the weight of water in 
pounds necessary to keep it full for one minute, then the leakage during 
filling is approximately 

«/ = fx*,; 



294 POWER PLANT TESTING 

and the clearance = {w\ — w') in pounds of water which can be readily 
reduced to cubic inches. 

The clearance for the crank end is found in the same general way as 
for the head end. 

Most engines have small holes at the top of the cylinder at each end 
(for double-acting engines) which lead into the clearance space. Holes 
which are covered by the piston on the dead-center would obviously be 
of no value. All water must of course be drained from each end before 
filling. Removing the cylinder head for packing the piston is the best 
method for observing with certainty that there is no water in the head 
end- The drip pipes in the cylinder can usually be relied on to remove 
water from the crank end. Determinations should be repeated several 
times, and the average value is to be used in calculations. 

RULES FOR CONDUCTING TESTS OF RECIPROCATING EN- 
GINES. A.S.M.E. CODE of 1912 1 

Determine the object, take the dimensions, note the physical conditions 
not only of the engine but of all parts of the plant that are concerned in 
the determinations, examine for leakages, install the testing appliances, 
etc., as pointed out in the general instructions given on pages 258 to 263, 
and prepare for the test accordingly. 

The apparatus and instruments required for a simple performance test 
of a steam engine, in which the steam consumption is determined by feed- 
water measurement, are: 

(a) Tanks and platform scales for weighing water (or water meters calibrated in 
place). 

(b) Graduated scales attached to the water glasses of the boilers. 

(c) Pressure gages, vacuum gages, and thermometers. 

(d) A steam calorimeter. 

(e) A barometer. 

(/) Steam engine indicators. 

ig) A planimeter. 

(h) A speed measuring device. 

(i) A dynamometer for measuring the power developed. 

Directions regarding the use and calibration of these appliances are 
given in the preceding chapters. 

The determination of the heat and steam consumption of an engine by 
feedwater test requires the measurement of the various supplies of water 
fed to the boiler; that of the water discharged by separators and drips 
not returned to the boiler, and that of water and steam which escapes 
by leakage of the boiler and piping; all of these last being deducted from 
the total feedwater measured. 

1 Journal of A.S.M.E., Nov., 1912. 



STEAM ENGINE TESTING 295 

Where a surface condenser is provided and the steam consumption is determined 
from the water discharged by the air pump, no such measurement of drips and 
leakage is required, but assurance must be had that all the steam passing into 
the cylinders finds, its way into the condenser. If the condenser leaks the de- 
fects causing it should be remedied, or suitable correction made for the leakage. 

To ascertain the consumption of heat, the various feed temperatures 
are taken and heat calculations made accordingly. If the conditions 
imposed by the particular method adopted for carrying on the test depart 
from the usual practice, as for example where a colder supply of feedwater 
is used than the ordinary supply, a preliminary or subsequent run should 
be made to ascertain the temperatures which obtain under the usual 
working conditions, and the heat measurements obtained under the test- 
conditions appropriately corrected for such departures. 

The steam consumed by steam-driven auxiliaries which are required 
for the operation of the engine should be included in the total steam from 
which the heat consumption is calculated and the quantity of steam thus 
used should be determined and reported. 

Duration. A test for heat or steam consumption, with substantially 
constant load, should be continued for such time as may be necessary to 
obtain a number of successive hourly records, during which the results are 
reasonably uniform. For a test involving the measurement of feed- 
water for this purpose, five hours is sufficient duration. Where a surface 
condenser is used, and the measurement is that of the water discharged by 
the air pump, the duration may be somewhat shorter. In this case, 
successive half-hour records may be compared and the time corre- 
spondingly reduced. 

When the load varies widely at different times of the day, the duration 
should be such as to cover the entire period of variation. 

The preliminary or subsequent trial for determining the working 
temperatures on a heat test, where the temperatures obtained under 
the test conditions depart from the usual temperatures, should be of 
such duration as may be required to secure working results. 

Starting and Stopping. The engine and appurtenances having been 
set to work and thoroughly heated under the prescribed conditions of 
test, except in case where the object is to obtain the performance under 
working conditions, note the water levels in the boilers and feed reservoir, 
take the time and consider this the starting time. Then begin the 
measurements and observations and carry them forward until the 
end of the period determined on. When this time arrives, the water 
levels and steam pressure should be brought as near as practicable 
to the same points as at the start. This being done, again note the 
time and consider it the stopping time of the test. If there are dif- 
ferences in the water levels, proper corrections are to be applied. 



296 POWER PLANT TESTING 

Where a surface condenser is used, the collection of water discharged 
by the air pump begins at the starting time, and the water is thereafter 
measured or weighed until the end of the test, no observations of the 
boilers being required. 

Care should be taken in cases where the activity of combustion in the boiler furnaces 
affects the height of water in the gage glasses that the same conditions of fire 
and drafts are operating at the end as at the beginning. For this reason it is 
best to start and stop a test without interfering with the regularity of the oper- 
ation of the feed pump, provided the latter can be regulated to run so as to 
supply the feed water at a uniform rate. In some cases where the supply of feed- 
water is irregular, as, for example, where an injector is used of a larger capacity 
than is required, the supply of feedwater should be temporarily shut off. 

Suitable care should be observed in noting the average height of the water in 
the glasses, taking sufficient time to satisfactorily judge of the full extent of 
the fluctuation of the water line, and thereby its mean position. 

Records. A set of indicator diagrams should be obtained at intervals 
of 10 or 20 minutes, and at more frequent intervals if the nature of the 
test makes it necessary. Mark on each card the cylinder and the end 
on which it was taken, also the time of day. Record on one card of each 
set the readings of the pressure gages concerned, taken at the same time. 
These records should subsequently be entered on the general log, together 
with the areas, pressures, lengths, etc., measured from the diagrams, 
when these are worked up. 

CALCULATION OF RESULTS 

(a) Dry Steam. The quantity of dry steam consumed when there is no superheating 
is determined by deducting the moisture found by calorimeter test from the 
total amount of feedwater (the latter being corrected for leakages) or from the 
amount of air-pump discharge, as the case may be. 

When there is superheating the dry steam is found by multiplying the weight 
of superheated steam by the factor 

, C v {T-t) 

1 + —^ (90) 

H - q 2 

in which 

C p = specific heat at constant pressure of superheated steam at observed 
pressure and temperature. 

T = temperature of superheated steam. 
t = temperature of saturated steam. 

H = total heat of saturated steam at the observed pressure. 

q 2 = total heat of feedwater. 

(b) Heat Consumption. The number of heat units consumed by the engine is found 
by multiplying the weight of feedwater consumed, corrected for leakages, by the 
total heat of the steam above the working feed temperature, and multiplying 
the product by a factor of correction expressing the quality of the steam. 

If the steam contains moisture, this factor equals 

* + P ? 5p- ! , <*> 

H -qt 



STEAM ENGINE TESTING 297 

in which x is the quality of the steam (one minus the decimal representing the 
percentage of moisture), P the proportion of moisture, qi the total heat of water 
at the temperature of the steam, q^ the total heat of the feedwater, and H the 
total heat of saturated steam at the observed pressure. 

If the steam is superheated, the factor is that given above under (a) Dry- 
Steam. 

If there are a number of sources of feedwater supply, the corresponding heat 
units should be determined for each supply and the various quantities added 
together. 

The British standard of heat consumption is based on a feedwater temper- 
ature assumed to be that of the temperature of saturated steam corresponding 
to the observed back pressure (whether this is above or below the atmosphere), 
plus the temperature due to heat derived from jacket or reheated drips. It 
does not include the heat consumed by any auxiliaries, except jackets and re- 
heaters. 

(c) Indicated Horse Power. In a single double-acting cylinder the indicated horse 
power is found by using the formula 

PLA N 
33,000 
in which P represents the average mean effective pressure in pounds per sq. in. 
measured from the indicator diagrams, L the length of stroke in ft., A the area 
of the piston less one-half the area of the piston rod, or the mean area of the 
rod if it passes through both cylinder heads, in sq. in., and N the number of 
single strokes of the engine per minute. 

Where extreme accuracy is required, the power developed by each side of the 
piston may be determined and the results added together. 

(d) Brake Horse Power. The brake horse power is found by multiplying the net 

weight on the brake arm (the gross weight minus the weight when the brake is 
entirely free) in pounds, the circumference of the circle passing through the bearing 
point at the end of the brake arm, in ft., and the number of revolutions of the 
brake shaft per minute; and dividing the product by 33,000. 

(e) Electrical Horse Power. The electrical horse power for a direct-connected gen- 
erator is found by dividing the output at the bus-bar, expressed in kilowatts, by 
the decimal 0.746. For alternating-current systems the net output is to be used, 
being the total output less that consumed for excitation. 1 

(J) Efficiency. The efficiency is expressed by the thermal efficiency ratio, which is 
found by dividing the quantity 2545 by the number of heat units consumed per 
h.p.-hr., either indicated or brake. 

(g) Steam accounted for by Indicator Diagrams. The steam accounted for, ex- 
pressed in pounds per i.h.p. per hour, may readily be found by using the formula 2 

^^ [(C + E)W C -(H + E) W h ], (92) 

m.e.p. 

in which 

m.e.p. = mean effective pressure, lbs. per sq. in. 

C = proportion of stroke completed at cut-off or release. 

E — proportion of clearance. 

H = proportion of stroke uncompleted at compression. 

W c = weight of 1 cu. ft. steam at cut-off or release pressure. 

Wh = weight of 1 cu. ft. steam at compression pressure. 

1 Calculation of electrical output is explained on pages 323 and 324. 

2 Compare with equation (98) page 312. 



298 POWER PLANT TESTING 

The points of cut-off release and compression, referred to are indicated in 
Fig. 299. 

In multiple expansion engines the mean effective pressure to be used in the 
above formula is the combined m.e.p. referred to the cylinder under consideration. 
In a compound engine the combined m.e.p. for the h.p. (high-pressure) cylinder 
is the sum of the actual m.e.p. of the h.p. cylinder and that of the l.p. (low- 
pressure) cylinder multiplied by the cylinder ratio. Likewise the combined 
m.e.p. for the l.p. cylinder is the sum of the actual m.e.p. of the l.p. cylinder and 
the m.e.p. of the h.p. cylinder divided by the cylinder ratio. 
(h) Cut-off and Ratio of Expansion. To find the percentage of cut-off, or what may 
best be termed the " commercial cut-off," the following rule should be observed: 

Through the point of maximum pressure during admission draw a line 
parallel to the atmospheric line. Through a point on the expansion line, where 
the cut-off is complete, draw a hyperbolic curve. The intersection of these 
two lines is the point of commercial cut-off, and the proportion of cut-off is 
found by dividing the length measured on the diagram up to this point by 
the total length. 

To find the ratio of expansion divide the volume corresponding to the piston 
displacement, including clearance, by the volume of the steam at the commer- 
cial cut-off, including clearance. 

In a multiple expansion engine the ratio of expansion is found by dividing the 
volume of the l.p. cylinder, including clearance, by the volume of the h.p. cylinder 
at the commercial cut-off, including clearance. 

TABLE 1. DATA AND RESULTS OF HEAT AND FEED WATER TESTS OF 

STEAM ENGINE, SHORT FORM, 

CODE OF 1912 

(1) Test of engine located at 

to determine conducted by 

(2) Type and class of engine and auxiliaries 

1st Cyl. 2d Cyl. 3d Cyl. 

(3) Dimensions of main engine: 

(a) Diameter of cylinder ins 

(b) Stroke of piston ft 

(c) Diameter of piston rod each end ins 

(d) Average clearance per cent 

(e) Cylinder ratio 

(/) Horse power constant for 1 lb. m.e.p. and 1 r.p.m 

(4) Dimensions and type of auxiliaries . 

(5) Date 

(6) Duration hrs. 

Average Pressures and Temperatures 

(7) Pressure in steam pipe near throttle by gage lbs. per sq. in. 

(7a) Absolute pressure in steam pipe near throttle lbs. per sq. in. 

(8) Barometric pressure of atmosphere in ins. of mercury 

(9) Pressure in receivers by gage lbs. per sq. in. 

(10) Vacuum in condenser in ins. of mercury 

(11) Pressure in jackets and reheaters by gage lbs. per sq. in. 

(11a) Temperature of steam near throttle deg. F. 



STEAM ENGINE TESTING 299 

(lib) Temperature of steam in steam chest deg. F. 

(12) Temperature of main supply of feedwater deg. F. 

(13) Temperature of additional supplies of feedwater deg. F. 

Total Quantities 

(14) Total water fed to boilers from main source of supply lbs. 

(15) Total water fed from additional supplies lbs. 

(16) Total water fed to boilers from all sources lbs. 

(17) Moisture in steam or superheating near throttle per cent or deg. F. 

(18) Factor of correction for quality of steam 

(19) Total dry steam consumed for all purposes lbs. 

Hourly Quantities 

(20) Water fed from main source of supply lbs. 

(21) Water fed from additional supplies lbs. 

(22) Total water fed to boilers per hour lbs. 

(23) Total dry steam consumed per hour lbs. 

(24) Loss of steam and water per hour due to drips from main steam pipes and to 

leakage of plant lbs. 

(25) Net dry steam consumed per hour by engine and auxiliaries lbs. 

(26) Net dry steam consumed per hour: 

(a) By engine alone lbs. 

(6) By auxiliaries lbs. 

Heat Data 

(27) Heat units per lb. of dry steam, based on temperature of Line 12 B.t.u. 

(28) Heat units per lb. of dry steam, based on temperature of Line 13 B.t.u. 

(29) Heat units consumed per hour, main supply of feed B.t.u. 

(30) Heat units consumed per hour, additional supplies of feed B.t.u. 

(31) Total heat units consumed per hour for all purposes B.t.u. 

(32) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. 

(33) Net heat units consumed per hour: 

(a) By engine and auxiliaries B.t.u. 

(b) By engine alone B.t.u. 

(c) By auxiliaries B.t.u. 

Indicator Diagrams 

1st Cyl. 2d Cyl. 3d Cyl. 

(34) Commercial cut-off in per cent of stroke 

(35) Initial pressure in lbs. per sq. in. above atmosphere 

(36)^Back pressure at lowest point above or below atmos- 
phere in lbs. per sq. in 

(37) Mean effective pressure in lbs. per sq. in 

(38) Steam accounted for by indicator in lbs. per i.h.p. per 

hour: 

(a) Near cut-off 

(b) Near release 

Speed 

(39) Revolutions per minute rev. 

(40) Piston speed in ft. per min ft. 



300 POWER PLANT TESTING 

Power 

(41) Indicated horse power developed by main engine cylinders: 

1st cylinder i.h.p. 

2d cylinder i.h.p. 

3d cylinder whole engine i.h.p. 

Whole engine i.h.p. 

(42) Brake horse power b.h.p. 

Economy Results 

(43) Heat units consumed by engine and auxiliaries per hour: 

(a) Per indicated horse power B.t.u. 

(6) Per brake horse power B.t.u. 

(44) Dry steam consumed per indicated horse power per hour: 

(a) By engine and auxiliaries lbs. 

(b) By main engine alone lbs. 

(c) By auxiliaries lbs. 

(45) Dry steam consumed per brake horse power per hour: , 

(a) By engine and auxiliaries lbs. 

(6) By main engine alone lbs. 

(c) By auxiliaries lbs. 

(46) Percentage of steam used by main-engine cylinders accounted for by in- 

dicator diagrams: 

(a) Near cut-off per cent 

(b) Near release per cent 

(47) Sample Diagrams 

TABLE 2. DATA AND RESULTS OF STEAM-ENGINE TEST— COMPLETE 
V FORM, CODE OF 1912 

(1) Test of engine located at 

to determine conducted by 

(2) Type of engine (simple, compound, or other multiple expansion; condensing 

or non-condensing) 

(3) Class of engine (mill, marine, electric, etc.) 

(4) Rated power of engine 

(5) Name of builders 

(6) Number and arrangement of cylinders of engine; how lagged; type of con- 

denser 

(7) Type of valves 

(8) Type of boiler 

(9) Kind and type of auxiliaries (air pump, circulating pump, feed pump; jackets, 

heaters, etc.) 

IstCyl. 2dCyl. 3d Cyl. 
(10) Dimensions of engine: 

(a) Single or double acting 

(6) Cylinder dimensions: 

Bore, ins 

Stroke, ft 

Diameter of piston rod, ins 

Diameter of tail rod, ins 



STEAM ENGINE TESTING 301 

(c) Clearance in per cent of volume displaced by- 
piston per stroke: 

Head-end, per cent 

Crank-end, per cent 

Average, per cent 

(d) Surface in sq. ft. (average) : 

Barrel of cylinder, sq. ft 

Cylinder heads, sq. ft 

Clearance and ports, sq. ft 

Ends of piston, sq. ft 

(c) Jacket surfaces or internal surfaces of cylinder 

heated by jackets, in sq. ft.: 

Barrel of cylinder, sq. ft 

Cylinder heads, sq. ft 

Clearance and ports, sq. ft 

Receiver jackets, sq. ft 

(g) Horse power constant for 1 lb. m.e.p. and 1 
r.p.m 

(11) Dimensions of boilers: 

(a) Number 

(b) Total grate surface sq. ft. 

(c) Total water heating surface sq. ft. 

(d) Total steam heating surface sq. ft. 

(12) Dimensions of auxiliaries: 

(a) Air pump <-. 

(b) Circulating pump 

(c) Feed pumps 

(d) Heaters 

(13) Dimensions of condenser 

(14) Dimensions of electric or other machinery driven by engine 

(15) Date 

(16) Duration hrs. 

Average Pressures and Temperatures 

(17) Steam pressure at boiler by gage lbs. per sq. in. 

(18) Steam pipe pressure near throttle, by gage lbs. per sq. in. 

(19) Barometric pressure of atmosphere in lbs. per sq. in 

(20) Pressure in first receiver by gage lbs. per sq. in. 

(21) Pressure in second receiver by gage lbs. per sq. in. 

(22) Vacuum in condenser: 

(a) In ins. of mercury ins. 

(b) Corresponding absolute pressure lbs. per sq. in. 

(23) Pressure in steam jacket by gage lbs. per sq. in. 

(24) Pressure in reheater by gage lbs. per sq. in. 

(24a) Temperature of steam at boiler deg. F. 

(24b) Temperature of steam near throttle deg. F. 

(24c) Temperature of steam in steam chest deg. F. 

(25) Superheat in steam leaving first receiver deg. F. 

(26) Superheat in steam leaving second receiver deg. F. 

(27) Temperature of main supply of feedwater to boilers deg. F. 

(28) Temperature of additional supplies of feedwater deg. F. 



302 POWER PLANT TESTING 

(29) Ideal feedwater temperature corresponding to the pressure of the steam 

in the exhaust pipe, allowance being made for heat derived from jacket 

or reheater drips (British Standard) deg. F. 

(30) Temperature of injection or circulating water entering condenser deg. F. 

(31) Temperature of injection or circulating water leaving condenser deg. F. 

(32) Temperature of air in engine room deg. F. 

Total Quantities 

(33) Water fed to boilers from main source of supply lbs. 

(34) Water fed from additional supplies lbs. 

(35) Total water fed to boilers from all sources lbs. 

(36) Moisture in steam or superheating near throttle per cent or deg. F. 

(37) Factor of correction for quality of steam, dry steam being unity 

(38) Total dry steam consumed for all purposes 

Hourly Quantities 

(39) Water fed from main source of supply lbs. 

(40) Water fed from additional supplies lbs. 

(41) Total water fed to boilers per hour lbs. 

(42) Total dry steam consumed per hour lbs. 

(43) Loss of steam and water per hour due to drips from main steam pipes and 

to leakage of plant lbs. 

(44) Net dry steam consumed per hour by engine and auxiliaries lbs. 

(45) Dry steam consumed per hour: 

(a) Main engine alone \ lbs. 

(6) Jackets and reheaters lbs. 

(c) Air pump lbs. 

(d) Circulating pump '. lbs. 

(e) Feedwater pump lbs. 

(/) Other auxiliaries lbs. 

(46) Injection or circulating water supplied condenser per hour cu. ft. 

Heat Data 

(47) Heat units per pound of dry steam, based on temperature of Line 27 B.t.u. 

(48) Heat units per pound of dry steam, based on temperature of Line 28 B.t.u. 

(49) Heat units consumed per hour, main supply of feed B.t.u. 

(50) Heat units consumed per hour, additional supplies of feed B.t.u. 

(51) Total heat units consumed per hour for all purposes .B.t.u. 

(52) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. 

(53) Net heat units consumed per hour: 

(a) By engine and auxiliaries B.t.u. 

(b) By engine alone B.t.u. 

(c) By auxiliaries •. B.t.u. 

(54) Heat units consumed per hour by the engine alone, reckoned from tem- 

perature given in Line 29 (British Standard) B.t.u. 

Indicator Diagrams 

1st Cyl. 2d Cyl. 3d Cyl. 

(55) Commercial cut-off in per cent of stroke 

(56) Initial pressure in lbs. per sq. in. above atmosphere 

(57) Back-pressure at mid-stroke above or below atmos- 

phere in lbs. per sq. in 



STEAM ENGINE TESTING 303 

(58) Mean effective pressure in lbs. per sq. in 

(59) Equivalent mean effective pressure in lbs. per sq. in.: 

(a) Referred to first cylinder 

(6) Referred to second cylinder 

(c) Referred to third cylinder 

(60) Pressures and percentages used in computing the 

steam accounted for by the indicator diagrams, 
measured to points on the expansion and com- 
pression curves: 

Pressure above zero in lbs. per sq. in. : 

(a) Near cut-off , 

(6) Near release 

(c) Near beginning of compression 

Percentage of stroke at points where pressures 

are measured: 

(d) Near cut-off 

(e) Near release 

(/) Near beginning of compression . . . . 

(61) Aggregate m.e.p. in lbs. per sq. in. referred to each 

cylinder given in heading 

(62) Mean back pressure above zero, lbs. per sq. in 

(63) Steam accounted for in lbs. per indicated horse power 

per hour: 

(a) Near cut-off 

(6) Near release 

(64) Ratio of expansion 

(65) Mean effective pressure of ideal diagram 1 lbs. per sq. in. 

(66) Diagram factor 1 

Speed 

(67) Revolutions per minute 

(68) Piston speed per minute ft. 

(69) Variation of speed between no load and full load r.p.m. 

(70) Fluctuation of speed on suddenly changing from full load to no load, meas- 

ured by the increase in the revolutions due to the change r.p.m. 

Power 

(71) Indicated horse power developed by main engine: 

1st cylinder i.h.p. 

2d cylinder i.h.p. 

3d cylinder i.h.p. 

Whole engine i.h.p. 

(72) Brake horse power b.h.p. 

(73) Friction i.h.p. by diagrams, no load on engine, computed for average speed, .i.h.p. 

(74) Difference between Lines 71 and 72 h.p. 

(75) Percentage of i.h.p. of main engine lost in friction per cent 

(76) Power developed by auxiliaries 2 i.h.p. 

1 See Journal of A.S.M.E., Nov., 1912, page 1861. 

2 These are not included in the power developed by the main engine. 



304 POWER PLANT TESTING 

Economy Results 

(77) Heat units consumed per indicated horse power per hour: 1 

(a) By engine and auxiliaries B.t.u. 

(b) By engine alone B.t.u. 

(78) Heat units consumed per brake horse power per hour: , 

(a) By engine and auxiliaries B.t.u. 

(6) By engine alone B.t.u. 

(79) Heat units consumed by engine per hour, corresponding to ideal temperature 

of feedwater given in Line 29, per indicated horse power (British 
Standard) B.t.u. 

(80) Dry steam consumed per i.h.p. per hour: 

(a) By engine and auxiliaries lbs. 

(b) By main engine alone lbs. 

(c) By auxiliaries lbs. 

(81) Dry steam consumed per brake h.p. per hour: 

(a) By engine and auxiliaries lbs. 

(6) By main engine alone lbs. 

(c) By auxiliaries lbs. 

(82) Percentage of steam used by main engine cylinders accounted for by indi- 

cator diagrams: 

1st Cyl. 2d Cyl. 3d Cyl. 

(a) Near cut-off '. 

(b) Near release 

Efficiency Results 

(83) Thermal efficiency ratio for engine and auxiliaries: 

(a) Per indicated horse power per cent 

(6) Per brake horse power per cent 

(84) Thermal efficiency ratio for engine alone: 

(a) Per indicated horse power per cent 

(6) Per brake horse power per cent 

(85) Ratio of economy of engine to that of an ideal engine working with the 

Rankine cycle (see page 308) per cent 

Work Done per Heat Unit 

(86) Ft.-lbs. of net work per B.t.u. consumed by engine and auxiliaries 

(1,980,000 -=- Line 78a) ft.-lbs. 

Note. Both the Short Form and Complete Form here given refer to a steam engine 
used for general service. 

For an engine driving an electric generator the form should be enlarged to include 
the electrical data, embracing the average voltage, number of amperes in each phase, 
number of watts, number of watt hours, average power factor, etc. ; and the economy 
results based on the electrical output embracing the heat units and steam consumed per 
electric h.p. per hour and per kw.-hr., together with the efficiency of the generator. 
See table for Steam Turbine Code, pages 325 to 328. 

Likewise, in a marine engine having a shaft dynamometer, the form should include 
the data obtained from this instrument, in which case the brake h.p. becomes the 
shaft h.p. 

1 The h.p. on which the economy and efficiency results are based are those of the main 
engine given in Line 71. 



STEAM ENGINE TESTING 305 

Surface condensers are usually perferred for accurate engine tests 
because the steam used by the engine can be determined directly by 
weighing or measuring the condensed steam. A surface condenser is 
essentially a vessel of considerable size in which there are a great many 
brass tubes. It is usually designed so that exhaust steam passes on its 
way through the condenser into contact with the outside surface of these 
tubes while cold water for condensing the steam circulates inside the 
tubes. Steam condensed in this way accumulates in the bottom of the 
condenser and is removed by an air pump used for producing a vacu- 
um, or by gravity if the pressure in the condenser is atmospheric, as 
it will be if the engine is operating " non-condensing," that is, without 
a vacuum. It is very essential, however, that surface condensers be 
tested for leakage, preferably before and after every important test is 
made; and the leakage should be determined with the same vacuum in the 
condenser as there is when it is used in the engine test. Probably the 
best method to determine the amount of condenser leakage is to pass 
cooling water through the tubes at the normal rate of flow, maintaining 
at the same time with the air pump the required vacuum. Then the 
amount of water removed by the air pump is the leakage of circulating 
water through the tubes into the steam space. Under normal operating 
conditions there would be no leakage of steam into the circulating 
water, because the water will be at a higher pressure than the steam. 

If only a test is to be made to determine whether or not there is any 
leakage in the condenser, the test most generally applied is to close 
all connections to the condenser and observe whether a vacuum once 
established can be maintained a reasonably long time. A more rapid 
test applicable, however, only where salt water is used for cooling, is 
to test the condensed steam several times during a test by adding a little 
silver nitrate to a small amount of the condensed steam. If there is no 
appreciable precipitate 1 it may be assumed that the condenser does not 
leak. 

Som'e of the important considerations to be observed in an accurate 
engine test will now be given as stated in the rules adopted by the Ameri- 
can Society of Mechanical Engineers. 

Discussion of Thermal Efficiency. The ratio of the heat converted 
into work to the heat supplied to the engine is called the thermal efficiency. 
The first of these quantities is calculated from the indicated horse power 
and the latter from the weight and total heat per pound of the steam 
supplied. The only uncertainty arises as to the proper base from which 
to calculate. The total heat of steam given in steam tables is calculated 
from 32 degrees Fahrenheit, but it is obvious if this base is adopted the 

1 The white precipitate formed with the salt in sea water is of course silver chloride, 
thus, AgN0 3 + NaCl = AgCl + NaN0 3 . 



306 POWER PLANT TESTING 

engine may be charged with more than its share of heat. If, for ex- 
ample, the exhaust steam from the engine passes through a feedwater 
heater and the engine returns the condensed steam to the boiler as 
feedwater at say 150 degrees Fahrenheit, then there will be 150 — 32, 
or 118 B.t.u. in every pound of steam passing continually from the 
engine to the boiler and from the boiler back to the engine without 
doing any work. More accurately, then, the thermal efficiency of an 
engine (E t ) should be stated as 

e, = 5^Q/ ( 93 ) 

where Q u and Q f are the heat equivalents respectively of the useful 
work and of the engine friction, while Q„ should be denned as the 
net heat supplied to the engine. From this discussion it follows that 
the more efficient the feedwater heater the higher the efficiency of 
the engine will be, and if an efficient heater is not used there is no 
reason for charging a loss to the engine. Obviously the limit to the 
amount of heat returnable to the boiler by means of a heater is the 
amount of heat in the exhaust steam, and this limit can be nearly ap- 
proached under actual practical conditions. It is, therefore, very reason- 
able that the " datum " for the calculation of the heat supplied to the 
engine should be the heat of the liquid corresponding to the temperature 
of the steam in the exhaust pipe from the engine. All this applies, 
of course, equally well to engines whether operating condensing or non- 
condensing. In other words, the net heat supplied to the engine is 
the total heat of the steam entering the engine, less the heat of the 
liquid at the temperature of the engine exhaust. 

The temperature of the exhaust must be taken by a thermometer in 
a suitable thermometer cup placed in the exhaust pipe close to the engine; 
and, similarly, the temperature and quality of the steam supplied to the 
engine must be determined by thermometers and a steam calorimeter 
placed close to, but on the boiler side of, the engine throttle valve. 

Fig. 303 shows diagrammatically the heat distribution and various losses 
in a steam plant, and gives approximate percentage values of the losses. 

Engine Performance Expressed in British Thermal Units. A method 
which is rapidly gaining in favor among practical engineers is to express 
the performance of a steam engine or turbine by the number B.t.u. 
supplied per indicated horse power per minute, the heat units supplied 
per minute being determined, as explained in the preceding paragraphs; 
that is, the total heat in the steam entering at the throttle less the heat 
of the liquid at the temperature of the exhaust. 

Hirn's Analysis. For certain scientific investigations it is useful to 
make a heat analysis of the indicator diagram, to show the interchange 
of heat from steam to cylinder walls, etc., which is going on within the 



STEAM ENGINE TESTING 



307 




308 



POWER PLANT TESTING 



cylinder. This is unnecessary for commercial tests. Years ago deduc- 
tions from such an analysis were considered to be of considerable impor- 
tance to designers; but, lately, such data are considered of very doubtful 
importance. 

Ratio of Economy of an Engine to that of an Ideal Engine. The cycle 
of the ideal engine recommended for obtaining this ratio is that which was 
adopted by the Committee appointed by the Civil Engineers of London, 
to consider and report a standard thermal efficiency for steam engines. 
This engine is one which follows the Rankine cycle where steam at a con- 
stant pressure is admitted into a cylinder having no clearance, and after 
the point of cut-off is expanded adiabatically to the back-pressure. In 
obtaining the economy of this engine the feed-water is assumed to be 
returned to the boiler at the exhaust temperature (Fig. 304). 




— >■ Volume 
Fig. 304. — Indicator Diagram for the Ideal Rankine Cycle. 

The ratio of the economy of an engine to that of the ideal engine is 
obtained by dividing the heat consumption per indicated horse power per 
minute for the ideal engine (called the " theoretical water-rate ") by 
that of the actual engine. 

Engine Performance Compared with the Rankine Cycle. In order 
to know how much the efficiency of an engine can be improved it is most 
desirable to compare the actual thermal efficiency, with the highest pos- 
sible efficiency. For steam engines the standard cycle for comparison 
is now generally taken as the Rankine cycle, 1 in which the operation of 
the engine is assumed to be perfect; that is, without clearance in the 
cylinder, initial condensation, leakage or radiation. The indicator dia- 
gram for the Rankine cycle is represented by Fig. 304. The steam is 
assumed to be supplied to the engine cylinder at constant pressure until 
the point of cut-off, after which it is expanded adiabatically down to the 

1 Years ago it was not unusual to make this comparison with the efficiency of the 
Carnot cycle as a basis. This efficiency of a heat engine, it will be remembered, is ex- 
pressed by the ratio of 7\ — T 2 to 7\ where 2\ is the absolute initial temperature and 
T% is the absolute final temperature. 



STEAM ENGINE TESTING 



309 



back pressure at which the engine is operated on the return stroke when 
the exhaust steam is swept out of the cylinder and returned as feed-water 
to the boiler at the temperature of the exhaust. The same Rankine cycle 
represented in Fig. 304 when shown by a so-called entropy-temperature 
diagram can be made simpler both for analysis and calculations. This 
other kind of diagram, the details of which are somewhat more difficult 
to understand, is universally used by steam turbine engineers and has for 
the problem in hand particular advantages. In this diagram, any sur- 
face represents accurately to given scales a quantity of heat. Absolute 
temperatures (T) are the ordinates, and entropies 1 (<f>) are the abscissas. 
Specific Heat of Superheated Steam. In modern practice super- 
heated steam often enters our calculations. The specific heat of steam 



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700 750 



Fig. 305. 



350 400 450 500 550 6C 
Temperature" P 
Mean Values of Specific Heat (C p ) of Superheated Steam Integrated from 
Knoblauch and Jacob's Data. 



varies with the temperature and pressure as shown in Figs. 305 and 306, 
giving values of the mean and the true specific heat at constant pressure 
(Cp), as determined by Knoblauch and Jakob. 2 

1 Entropy, which Perry calls the " ghostly quantity," has no real physical significance, 
so that complete definition is not possible. If dQ is a small amount of heat added to a 
body and T is the absolute temperature at which the heat is added, then the change in 
entropy of that body is dQ/T, or d<f>— dQ/T. Entropy of saturated steam above the 
entropy of water at the freezing point is easily calculated. For saturated steam at 
any pressure, then 4> = xr/T + 6, where x is the quality of the steam, r is the heat of 
vaporization, T is the absolute temperature, and 6 is the entropy of the liquid (water). 

2 Zeit. Verein deutscher Ingenieure, Jan. 5, 1907. Values of mean specific heat 
are taken from Mechanical Engineer, July, 1907, and Professor A. M. Greene's paper 
in Proc. American Society of Mechanical Engineers, May, 1907. 



310 



POWER PLANT TESTING 



True specific heat represents the ratio of the amount of heat to be 
added to a given weight of steam at some particular condition of tem- 
perature and pressure to raise the temperature one degree to that re- 
quired to raise the temperature of water at maximum density one degree. 
The mean specific heat is almost invariably used in steam engine and 
turbine calculations. 



0.90 




200 250 

Temperature °C. 



Fig. 306. — Values of the "True" Specific Heat of Superheated Steam. 



Approximate Steam Consumption Calculated from an Indicator 
Diagram. It is often very convenient to be able to calculate the approxi- 
mate steam consumption of a steam engine from the data obtainable 
from an indicator card, the size of the piston, the stroke, and the speed. 
Using a double-acting, engine, the following symbols 1 may be used: 

1 Compare with Power, September, 1893. 



STEAM ENGINE TESTING 311 

p = mean effective pressure, pounds per square inch from indicator 

diagram. 
1 = length of the stroke of the engine in feet. 
a = area of the piston in square inches. 
b = percentage of clearance to the length of the stroke. 
c = percentage of stroke at any point in the expansion line. 1 
n = number of revolutions per minute; and 120 n = number of strokes 

per hour. 
w = weight of a cubic foot of steam having a pressure as shown by the 

indicator diagram corresponding to that at the point in the 

expansion line selected for c, pounds. 
w' = weight of a cubic foot of steam corresponding to the pressure at the 
"" end of compression, pounds. 

. -^" . — la (b + c) 

Then the number of cubic feet per stroke = — ■— {- in the clearance 

144(100) 

and piston displacement volumes (at c). 

Weight of steam per stroke, pounds = -, ~ (04) 

144 (100) v ^ y 

Volume of the clearance, cubic feet = 



144 (100) 

Weight of steam in clearance, pounds remaining in the cylinder 

= law'(b) t , 
144(100)*' 

Approximate net weight of steam used per stroke 

law (b + c) law' (b) la r/ , . , , n , N 

= —, x 7-^A = [(b + c) w - bw']. . (95) 

144(100) 144(100) 14,400 J y ^ OJ 

Approximate weight of steam from diagram per hour 

= i2onla _ bw , } 

14,400 lK y 

Indicated horse power for a double-acting engine 

= ^- n (97) 

33,000 

1 In other words this is the percentage of the entire stroke which has been swept 
through by the piston corresponding to the point in the expansion curve selected for 
measurements. It is preferable, however, to take this point not very far from the 
point of cut-off, since the assumption must be made that the product of pressure times 
volume in the expansion curve is constant, which is, of course, not accurate, and the 
error becomes greater as the expansion increases. 



312 



POWER PLANT TESTING 



Steam consumption per indicated horse power 1 is (96) divided by 
(97) or 



137.5 



[(b+c)w-bw' 



(98) 



Compare this with formula (92) page 297. 

The difference between the theoretical steam consumption calculated 
by the formula and the actual consumption as determined by tests 
represents steam " not accounted for by the indicator," due to cylin- 
der condensation, leakage 
through ports, radiation, 
etc. If the steam supplied 
to the engine is very wet, 
corrections for this moisture 
should be made in the value 
of w. 

Willans Law. One of the 
most serviceable checks that 
can be applied to engine 
tests is plotting the Willans 
line of total steam consump- 
tion per hour. Curve sheets 
illustrating this as plotted 
from actual tests by Barra- 
clough and Marks 2 are shown 
in Fig. 307. It will be ob- 
served that the points repre- 
senting the weight of steam 
used per hour when plotted 
for the horse power corre- 
sponding are on a straight line. In other words Willans law is usually 
stated thus: " With a fixed cut-off and a throttling governor the total 
steam used by the engine per hour at different loads can be represented 
by a straight line upon a mean effective pressure base or upon a horse- 
power base." - It will be shown also in the following paragraphs how, 
theoretically, this relation holds for an engine operating at a fixed cut- 
off and with a throttling governor and that the total steam used per 
hour is proportional to the mean effective pressure and also to the horse 
power developed. 

1 A method of determining steam consumption by means of logarithmic curves of 
indicator diagrams by J. P. Clayton is described in Bulletin No. 65 of Engineering Ex- 
periment Station of University of Illinois and in abridged form in Journal of A.S.M.E., 
April, 1912. 

2 Proceedings Institution of Civil Engineers, vol. 120, page 323. 



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Indicated Horse Power 

307. — "Willans" Lines for an Engine with a 
Throttling Governor. 



Pi 



STEAM ENGINE TESTING 313 

If we assume that the expansion curve is hyperbolic, which is usually 
near the truth, then the mean " forward " pressure given by an indicator 
diagram is 1 

f±^} (9.) 

where pi is the initial pressure of the steam and r is the ratio of expansion. 
With a throttling governor r is of course constant. The terms in the 
parenthesis can then be represented by a constant c and the mean forward 
pressure p/ then can be written as piC. Volume of steam used per 
hour for a double-acting engine can be expressed in cubic feet as 120 (nV), 
where n is the number of revolutions per minute and V is the volume 
of steam admitted to the cylinder per stroke. Now if we use the symbol 
Vi for the specific volume, that is, the volume in cubic feet of a pound 
of steam at the pressure pi, and assuming for a small range of pressures 
that piVi = a constant k, then we can write, if W is the weight of steam 
used per hour in pounds, 

= 120 (nV) _ 120 (nV Pl ) 

Vi k v ' 

Now with a throttling governor and constant cut-off all these quantities 

are constant except pi, and writing a constant z for the term ~ — - 

we have W = zpi, but it was shown above that the mean forward pres- 
sure p/ = cpi, so that W = z — • 

So that the curve representing this equation is a straight line and passes 
through the origin of coordinates. If, however, we use the mean 
effective pressure instead of the mean forward pressure, then 
m.e.p. = p/ - p6, 

where p& is the mean " back " or exhaust pressure: In these last terms 
then 

W = - (m.e.p. + p&) (101) 

This last equation may be stated as W = a constant X m.e.p. + 
another constant which, when plotted to a scale of mean effective pres- 
sure for abscissas and weight of steam used per hour for ordinates, is 
also a straight line, intersecting the axis of ordinates above the origin at 
a distance corresponding to the steam consumption per hour at no load. 
Since the indicated horse power (i.h.p.) is proportional to mean 
effective pressure, a straight line will result when the steam consumption 
and indicated horse power are plotted; and the same holds true also 

1 Compare with Perry's " Steam Engine," page 286. 



314 POWER PLANT TESTING 

when steam consumption is plotted with brake horse power (b.h.p.) 
instead of indicated horse power. 

Curves Showing Results of Tests Graphically. One of the best 
checks of an engine test is to plot the principal observations graphically 
as the test proceeds. This is particularly important as regards the 
total weight of steam used per hour. For a series of tests each made 
with a different load the points plotted with horse power (either indicated 
or brake) as abscissas and total steam per hour as ordinates should 
lie along a straight line, known as the Willans line. This statement 
applies accurately only for engines operating with a throttling governor 
at, of course, constant speed, but is generally applicable to steam 
turbine tests, irrespective of the type of governor. 



CHAPTER XIII 

TESTING STEAM TURBINES AND TURBO-GENERATORS 

Testing Steam Turbines. 1 In every power plant the means should be 
available for making tests of the steam equipment to determine the steam 
consumption. Usually tests are made to determine how nearly the 
performance of a turbine approaches the conditions for which it was 
designed. The results obtained from tests of a turbine are to show usually 
the steam consumption required to develop a unit of power in a unit of 
time, as, for example, a horse power^or a kilowatt-hour. 

In such tests a number of observations must be made regarding the 
condition of the steam in the passage through the turbine and of the per- 
formance of the turbine as a machine. To get a good idea of what these 
observations mean, it may be profitable to follow the steam as it passes 
through the turbine. The steam comes from the boilers through the 
main steam pipe and the valves of the turbine to the nozzles or stationary 
blades as the case may be. It then passes through the blades and finally 
escapes through the exhaust pipe to the condenser. It is preferable to 
have a surface condenser for tests, so that the exhaust steam can be 
weighed. The weighing is preferably done in large tanks mounted on 
platform scales. 

Methods for Testing. The important observations to be made in 
steam turbine tests are: 

1. Pressure of the steam supplied to the turbine. 

2. Speed of rotation of the turbine shaft, usually taken in revolutions 
per minute. 

3. Measurement of power with a Prony or a water brake, if the power 
at the turbine shaft is desired; or with electrical instruments (ammeters, 
voltmeters, and wattmeters), if the power is measured by the output 
of an electric generator. 

4. Weight, or measurement by volume, of the condensed steam dis- 
charged from the condenser. Unless a surface condenser is used it is very 

1 Tests of the turbines alone in a modern station may be only a rough indication of 
the over-all economy of the plant. Recently steam turbines were installed in a large 
power plant where they replaced steam engines of an excellent make. Tests of the 
turbines and of the engines made without considering the losses in the rest of the plant 
showed very little gain in efficiency by this change, although it was found that the fuel 
consumption was reduced twenty per cent. 

Parts of this chapter and the chapter following are taken from the author's work on 
"The Steam Turbine" (John Wiley & Sons, New York). 

315 



316 



POWER PLANT TESTING 



difficult to obtain the amount of steam used by the turbine. All leakages 
from pipes, pumps, and valves, which are a part of the steam which has 
gone through the turbine, must be added to the weight of the condensed 
steam. The accuracy of a test often depends a great deal on how ac- 
curately leaks have been provided against, or measured when they occur. 

5. Temperature of the steam as it enters the turbine. 1 

6. Vacuum or back-pressure in the exhaust pipe of the turbine. 

All gages, electrical instruments, and thermometers should be carefully 
calibrated before and after each test, so that observations can be corrected 
for any errors. The zero readings of Prony and water brakes for measur- 
ing power should be carefully observed and corrected to eliminate the 
friction of the apparatus with no load. Unless all these precautions are 
taken the difficulties in getting reliable tests of turbines are greatly 
increased. In all cases tests should be continued for several hours with 

absolutely constant conditions if 
the tests are to be of value. 

The most valuable test of a 
steam turbine or of a reciprocat- 
ing steam engine is made when 
varying only the load; that is, 
with pressures, superheat, and 
speed constant. When the steam 
consumption is then plotted 
against fractions of full load, a 
water-rate curve is obtained. For 
such a curve a series of tests] are 
needed, each for some fraction of 
full load; and in each separate 
test the power as well as all the 
other conditions must be held con- 
stant. 

Another important test of the 
performance of a steam turbine is 
made by varying both the speed 
and the power and keeping the 
other conditions constant. The observations of speed and power from 
such a test give a power parabola as illustrated in Fig. 308. This curve 
shows at what speed the turbine gives the greatest output. 

1 The most satisfactory tests of turbines are made with steam slightly superheated 
rather than wet. When steam is very wet (more than about 4 per cent moisture for 
ordinary pressures) the determination of the quality is difficult. There is also a danger 
that steam showing only a few degrees of superheat by the reading of the thermometer 
is actually wet. The high temperature is due in such cases to heating from eddies 
around the thermometer case or in steam pockets near it. 



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800 1200 16C 
Speed E.P.M. 



Results of Tests of a Turbine at 
Various 



STEAM TURBINES AND TURBO-GENERATORS 317 

Tests may also be made with varying initial steam pressure, but keep- 
ing other conditions including exhaust pressure and load constant. 

Calculations of the steam consumption and efficiency of turbines made 
by allowing for the different losses as calculated separately and then 
added together as is often done to determine the losses in electrical 
apparatus are of very little value except when made by experienced 
designers. 1 

Commercial Testing. The methods used by the New York Edison 
Company in commercial tests of steam turbine-generator units may well 
be explained briefly. 

During a test the load on the turbine unit is maintained as constant 
as possible by " remote control " of the turbine governor by the switch- 
board operator. The maximum variation in load is to be held within 4 
per cent above and below the mean. For some time previous to the test 
the turbine is run a little below the load required for the test, but at least 
ten minutes before the starting signal is given the test load must be on 
the machine. 

Three-phase electrical load is measured by the two-wattmeter method, 2 
using Weston indicating wattmeters of the standard laboratory type. 
These instruments are calibrated at a well-known testing laboratory 
immediately before and after the test. Power factor is maintained 
substantially at unity and all electrical readings are taken at one-minute 
intervals. 

When the turbine is supplied with a surface condenser, the steam con- 
sumption, or water rate, is determined by weighing in a large tank sup- 
ported on platform scales the condensed steam delivered from the 
condenser hot well. Above the tank on the scales a reservoir is provided 
which is large enough to hold the condensation accumulating between 
the weighings, which were made at intervals of five minutes. By using 
a loop connection for the gland water supply (of Westinghouse turbines) 
or the water from the step bearing (of Curtis turbines, using water for 
this bearing) the necessity for correcting the weighings for these amounts 
is avoided. 

Because the circulating water at the stations of this company is usually 
quite salty, any condenser leakage is detected by testing the condensed 
steam by the silver-nitrate test with a suitable color indicator. This 
color method is said to be a decided advantage over the usual method of 
weighing the leakage accumulating during a definite period when the 

1 This method of calculation of steam consumption is explained in detail in " The 
Steam Turbine," by the author, pages 86-93. Steam consumption of a turbine can be 
predicted by calculations much more accurately than for a steam engine. 

2 See Kent's " Mechanical Engineer's Pocket-Book," 8th Ed., page 1396, or Foster's 
" Electrical Engineer's Pocket-Book," 4th Ed., pages 51 and 325. 



318 POWER PLANT TESTING 

condenser is idle and tested only with full vacuum. By taking samples 
of circulating water and condensed steam at the same time, it is possible 
to detect any change in the rate of condenser leakage. 

The water level in the hot well is maintained at practically a constant 
point by means of a float valve in the well, automatically controlling the 
speed and, therefore, the amount of the delivery of the hot-well pump. 
This device avoids the necessity for the difficult correction to be made in 
a test when the levels in the hot well are not the same at the beginning 
and end of a test. Temperatures and pressures of the admission steam 
are determined by mercury thermometers and pressure gages located 
near the main throttle valve of the turbine; the amount of superheat is 
determined by subtracting from the actual steam temperature after 
making thermometer connections the temperature of saturated steam 
corresponding to the pressure at the point where the temperature is 
measured. All gages and thermometers are calibrated before and after 
the test. 

Vacuum is measured directly at the turbine exhaust by means of a 
mercury column with a barometer alongside for reducing the vacuum to 
standard barometer conditions (30 inches). By this latter arrangement 
the necessity for temperature corrections between the two mercury 
columns not at the same place is avoided. 

It has sometimes happened that split condenser tubes have caused a 
leakage of steam which was extremely difficult to measure. Cases are 
reported where the split opened up only when the condenser was heated 
with a large volume of steam. On this account it is preferable not to 
use a leaky condenser for accurate tests; in other words, the condenser 
should be thoroughly repaired before tests are made. The effect of split 
tubes causing an irregular amount of leakage is usually shown in tests by 
inconsistent results in the weight of condensed steam. In that case the 
leakage will be greatest with largest flow of steam through the condenser 
and it will be observed, for an engine operating with a throttling governor 
or with a steam turbine, that when the " Willans line " page 274, is 
drawn to check the tests that it will be curved instead of straight. It 
should be noted, however, that a curved " Willans line " does not neces- 
sarily indicate this phenomenon in condenser leakage, as the irregularity 
may be due to faulty design of the engine 1 or turbine. Tests of condensers 
for leakage should be run long enough so that the quantity of water 
coming through can be determined with accuracy. 2 Usually a leakage 
test run for less than an hour or two is of no use at all. 

1 The " Willans " line for a reciprocating engine operating with an automatic cut- 
off governor is usually a curve slightly concave upward. 

2 To determine accurately the weight of condensed steam the air-pump, piping, 
and tanks must be free from leaks, and the condenser and pump should be so arranged 



STEAM TURBINES AND TURBO-GENERATORS 319 

When the method of determining the weight of condensed steam by 
weighing the boiler feed-water is used the chances of error are very great 
and every possible precaution to insure accuracy must be observed. In 
the first place valves no matter how good should not be relied on to pre- 
vent the passage of steam through them. For this reason careful en- 
gineers insist on disconnecting from the line of steam piping between the 
boilers and the engine or turbine tested all other piping connected to it, 
and then blanking off with flanges all the sections disconnected. If 
flanged pipe fittings have been used in the pipe lines, blanking off sections 
in the various pipes is very easily accomplished by disconnecting the 
flanges and inserting a thin iron or copper plate with holes around the 
edge to fit the bolt-holes in the flanges. The plate is then easily bolted 
in place. Another important precaution to observe is that the outlets 
of all drain or drip pipes and of all blow-off valves must be visible. It is 
equally important that all the piping between the boiler feed-pumps and 
the boilers is exposed with all branches blanked off or plugged. Boiler 
leakage should be determined before and after each test with preferably 
the pipe supplying the turbine blanked off at the throttle valve, although 
if the throttle valve is reasonably tight the precaution of blanking off 
this valve is not considered so important as the others mentioned. In 
tests for boiler leakage the required steam pressure must be maintained 
on both the piping and the boilers. Measuring feed-water with water 
meters should not be thought of unless only approximate results are 
expected, and in that case such an arrangement is only allowable if the 
temperature of the boiler feed is not over 80 to 90 degrees Fahrenheit for 
most meters, and a by-pass at the meter is provided, so that at frequent 
intervals the meter can be calibrated by actual weighing of the flow 
through it, with the rate of flow and temperature of the water the same 
as in the tests. Boiler leakage is often as much as from ten to fifteen 
per cent of the weight of feed-water, and in some reliable tests a still 
greater leakage has been observed. 

Steam Consumption Determined by a " Heat Balance " Method. 
There is still another method sometimes used for determining the steam 
consumption of engines and turbines operated with jet condensers or 
condensers of a similar type where the cooling water and condensed steam 
are mixed and discharged together from the condenser. This method 
is based on the measurement of the amount of heat absorbed by the 
cooling water from the condensed steam. The weight w c and tempera- 
ture of the cooling water leaving the condenser t 2 , the quality of the 
exhaust steam x and the temperature of the mixture of condensed steam 
and cooling water t" are determined as accurately as possible and from 

with respect to each other that the condensed steam will flow in a continuous stream to 
the pump and into the tanks. 



320 POWER PLANT TESTING 

these data the weight of condensed steam w fi is of course readily calculated 
by a simple algebraic equation as follows: 

w c (t 2 - 32) + w 3 (q + xr) = (w c + w 8 ) (t" - 32), . . (102) 

where q and r are respectively the heat of the liquid and the heat of 
vaporization corresponding to the temperature of the exhaust steam. 
In this equation " heat contents " are measured for each term from 32 
degrees F. The method is, however, unreliable, and at best can be 
depended on for only very approximate results. The reason for this 
inaccuracy is the difficulty of measuring, especially in large plants, the 
quantity of cooling water and the true average temperature of a large 
volume of water flowing in a pipe or channel. It is found usually that 
the temperature of the water discharged from the condenser will vary 
from one side of the pipe to the other, and small errors in the determina- 
tion of this temperature, because the rise in temperature is small, will 
make large discrepancies in the calculated weight of condensed steam. 

Steam Consumption of Auxiliaries by Calculation of Heat Balance. 
The heat balance method of the preceding paragraph can be adapted 
also to the calculation of the steam used by non-condensing auxiliaries 
discharging their^exhaust into a feed-water heater, provided of course all 
the steam entering the heater is condensed. 

w = weight of condensed steam from turbine, lbs. 
Wo = weight of make-up water, lbs. 
w a = weight of steam used by auxiliaries, lbs. 
ti = temperature of water entering heater, deg. F. 
t 2 = temperature of water leaving heater, deg. F. 
to = temperature of make-up water, deg. F. 

t a = temperature of steam corresponding to back-pressure, deg. F. 
1 r a = heat of vaporization, corresponding to back-pressure, B.t.u. 
per lb. 
W (t a - ti) + wo (ta - to) = w a (r a + U - t 2 ). . . (103) 

Stage pressures should be observed and recorded when tests are 
made of steam turbines having a series of pressure stages. These data 
are often extremely useful, both for checking the weight of condensed 
steam if the turbine is of the nozzle type 1 and also for showing any 
abnormal conditions in the several stages. 

Results calculated \>n a basis of kilowatts output should be net; 
that is, the power required for excitation should be substracted from 

1 Usually the nozzles discharging the steam into the second stage of the turbine 
are always open, so that the total area is always constant. If, therefore, the areas of 
the smallest sections of these nozzles are measured and the pressure is observed in the 
first stage, the weight can be calculated with a considerable degree of accuracy by 
using the formula for the flow of steam on page 189. 



STEAM TURBINES AND TURBO-GENERATORS 321 

the generator output. If, however, the generator is self-exciting the 
net output can be measured directly at the terminals of the machine. 

" Guarantee '' tests of steam engines and turbines should be made 
under conditions as nearly as possible the same as that for which the 
turbine was designed. Different machines will have different correction 
factors for varying conditions of pressure, superheat, vacuum, etc., so 
that water rates corrected for large variations are always likely to be 
more or less inaccurate. This is particularly true in respect to vacuum 
corrections. Some turbines will give a very good efficiency with a low 
vacuum, but at a high vacuum because of an insufficiently large steam 
space the efficiency will be low. 

Heat Unit Basis of Efficiency 

A thermal efficiency can be calculated readily by determining what 
percentage the heat equivalent of the work is of the heat " used by the 
turbine," assumed to be the difference between the total heat in the steam 
at the initial conditions and the heat of the liquid in the condensed 
steam at the temperature of the exhaust. 

By this method the full-load test of a Westinghouse-Parsons turbine 
reported by F. P. Sheldon & Co., will be calculated from the data given 
in an official report. 

In order to make the results of such calculations of steam turbine 
tests comparable with the usual heat unit computations of reciprocating 
steam engine tests the results are often expressed in terms of indicated or 
"internal " horse power. It was assumed the mechanical efficiency of 
a reciprocating engine of about the same capacity at this load was about 
93.3 per cent. 

THERMAL EFFICIENCY OF A 400-KILOWATT STEAM TURBINE 

Brake horse power 660 

Corresponding indicated or " internal " horse power of a reciprocating 

engine = 708 

& .933 

Total steam used per hour, pounds 9169 

Steam used per " internal " horse power per hour, pounds 12.96 

Steam used per " internal " horse power per minute, pounds 0.216 

Steam pressure, pounds per square inch, absolute 166 . 9 

Superheat, degrees Fahrenheit 2.9 

Vacuum, referred to 30 inches barometer, inches 28 .04 

Temperature of condensed steam, degrees Fahrenheit (at .96 pound per square 

inch absolute pressure) = 100 . 6 

Total heat contents of one pound of dry saturated steam at the initial pres- 
sure, B.t.u 1193.9 

Heat equivalent of superheat in one pound of steam, B.t.u. (C p from Fig. 

305, page 309) . 1.9 



322 POWER PLANT TESTING 

Total heat contents of one pound of superheated steam, B.t.u 1195.8 

Heat of liquid in condensed steam, B.t.u 68 . 6 

Heat used in turbine per pound steam, B.t.u 1127.2 

Heat used in turbine per " internal " horse power per minute, B.t.u (1127.2 

L X 0.216) 243 .5 

33 000 

Heat equivalent of one horse power per minute, B.t.u. = — ' 42.42 

Thermal efficiency, per cent (42.42 -r- 243.5) 17.4 

CALCULATION OF EFFICIENCY (SHAFT AND BUCKET) OF A STEAM 
TURBINE GENERATOR COMPARED WITH THE RANKINE CYCLE. 

1. " Electrical " kilowatts. 

2. R.P.M. 

3. Steam per hour (corrected for moisture). 

4. Water rate per " electrical " kilowatt, pounds per hour. (3) -5- (1). 

5. PR, loss in generator, kilowatts. 

6. Rotation loss of generator alone, kilowatts. 

7. Rotation loss of wheel and generator, kilowatts. 

8. " Shaft " kilowatts. (1) + (5) + (6). 

9. " Bucket » kilowatts. (1) + (5) + (7). 

10. Water rate per " shaft " kilowatt, pounds per hour. 

11. Water rate per " bucket " kilowatt, pounds per hour. 

12. Steam-chest pressure, pounds per square inch, absolute. 

13. Exhaust pressure, pounds per square inch absolute. 

14. Available energy, B.t.u. 

44200 

15. Theoretical water rate, pounds per kilowatt hour, B.t.u. = — — — — — • 

Avail. En. (14) 

16. "Shaft" efficiency = (15) -i- (10). 

17. "Bucket" efficiency = (15) -*- (11). 

Notes. — For calculating rotation loss of a new design, stage pressures are of course 
used. 

Steam per hour is usually calculated from the area of the nozzles in the first stage if 
the governor is not operating. For a speed-torque test the flow of steam is constant and 

kw. for determining items (8) and (9) are read from this curve I kw. = X r.p.m. 

\ r.p.m. 

The speed output curve (Fig. 308, page 316) is very useful to engineers to 
determine if a turbine is running at its best speed. If the corresponding 
curves of steam consumption per kilowatt output (usually called water 
rate per kilowatt) and efficiency curves are calculated according to 
the above form a great deal of information is obtained about the 
operation and economy of a turbine. The torque line in Fig. 308 is 
always drawn straight, just as a " Willans line." A curve of total steam 
consumption is usually a straight line for the normal operating limits 
of a turbine, but usually becomes curved when a by-pass valve opens 
on overload, or when the turbine is over its capacity so that the pressures 
are not normal in the stages. 



STEAM TURBINES AND TURBO-GENERATORS 323 

The torque line shows why a turbine engine is not adaptable to auto- 
mobiles. The starting torque of a small commercial turbine is not 
large, so that starting would be difficult with a small wheel, and reversing 
and speed reduction would be as difficult as with a gasoline engine. 
The reciprocating steam engine as well as the gasoline engine has, there- 
fore, advantages over the steam turbine for this service. 

Electrical Output of Turbine Generators. Measurement of Direct 
Current. Careful engineers will not ordinarily use the instruments on 
the switchboard of a power station for measuring the electrical output 
of & generator, because, unless exceptional precautions have been 
taken to avoid " stray " magnetic fields and the instruments have been 
calibrated in place under operating conditions with a sufficient interval 
of time between observations of current (amperes) at different loads so 
that the shunts of the ammeters will reach a constant temperature for 
the particular value of current flowing there may be considerable error 
in the observations. Switchboard voltmeters are usually satisfactory 
if they are carefully calibrated; but the shunts of the type of ammeters 
ordinarily used have approximately only 60 millivolts drop, so that 
the indicating part of the ammeter must be almost entirely a circuit 
of copper wire. It is for this reason that such instruments are likely 
to be affected considerably by varying room temperatures, and with 
some shunt arrangements they are susceptible to errors, also from 
variations in the value of the circuit itself. For accurate measure- 
ments, it is therefore best to use only the portable types of indicating 
ammeters having shunts of 200 millivolts 1 drop. In these latter instru- 
ments the indicating part is made up largely of resistance wires having 
practically no temperature coefficient. Portable voltmeters are also to 
be preferred to those on the switchboards. 

Unless standard shunts of 200 millivolts drop as provided for good port- 
able ammeters are used the influence of " stray " magnetic fields must 
be guarded against. When on the other hand switchboard instruments 
are used, such influences must be investigated and arrangements must 
be devised so that " stray " fields will not affect the measurements. The 
influence of very weak magnetic fields can be eliminated from the final 
results by turning the instruments between successive readings. Obser- 
vations of current (amperes) made with the switchboard type of instru- 
ments are also often in error due to thermo-electric effects producing 
a small electromotive force sufficient, however, to alter the readings of 
the millivoltmeter. The error due to this cause can be observed by 
reading the millivoltmeter at the close of the test immediately after the 

1 This value for the drop in shunts is an arbitrary value selected by a number of 
makers of electrical instruments because it gives the best compensation of all the tem- 
perature errors. See General Electric Review, February, 1911. 



324 POWER PLANT TESTING 

current has been shut off in the main circuit. It should be, of course, 
the object of the observer to take this reading before the shunts and 
leads have cooled appreciably. If there is an error due to this cause 
there will be a small positive or negative deflection of the needle from the 
correct zero, which should be applied as a correction to all the observations 
of current. 

Measurement of Alternating Current. The same general precautions 
outlined above for direct-current instruments must be observed in 
the use of those for alternating current. Although steady magnetic fields 
are not often a cause of much trouble, it happens often, particularly 
in the case of large generators, that there are large magnetic fields in- 
fluencing the measuring instruments, which have the same frequency 
as that of the current measured. To eliminate the effect of such " stray " 
fields shielded types of instruments should be used. Only with the 
most expert handling can accurate results be expected when unshielded 
instruments are used. For measuring large values of alternating 
current, instrument transformers are generally used. These should be 
of the precision type and should be sent to a standardizing laboratory 
before and after a series of tests to be calibrated, and a certificate of 
accuracy should be obtained. The transformers should be calibrated 
at as nearly as possible the values of the current to be measured in the 
tests. 

Whenever it is possible tests of generators should be made with a non- 
inductive load, water rheostats being usually the most satisfactory 
apparatus for providing such a load. At least tests should be made under 
conditions giving a low power factor, so that there can be no error in 
the readings of the instruments due to phase displacements in the in- 
strument transformers. With a purely non-inductive load the readings of 
the ammeters and the voltmeters can be used to check the wattmeters. 
Although the readings of the wattmeters should be taken as the correct 
value of the output the apparent power as indicated by the ammeters 
and voltmeters should agree with the wattmeter readings within one per 
cent. If a non-inductive load cannot be secured the switchboard am- 
meters and voltmeters will be satisfactory for readings to indicate whether 
or not the load on the circuits is properly balanced. Watt-hour meters 
are not usually satisfactory for the accuracy expected in most tests, 
and the use of these instruments should be generally avoided. It is 
only in the case where tests must be made under extremely variable 
service conditions, where it is difficult to obtain a true average from the 
readings of indicating instruments, that a watt-hour meter, either for 
direct or for alternating current, may sometimes give more accurate 
results than the portable indicating types of instruments. Whenever 
watt-hour meters are used in tests they should be checked in place 



STEAM TURBINES AND TURBO-GENERATORS 325 

for a series of constant loads at the frequency, voltage, etc., which are 
to be used in the test. 

Single-phase indicating instruments are to be preferred for measure- 
ments of polyphase current to the standard types of so-called polyphase 
instruments. The reason for this preference is that the indications 
of a polyphase instrument are produced by two influences from separate 
phases of the current in such manner that a correction cannot be applied 
to obtain true values unless the division of the load is determined by the 
use of single-phase instruments. Obviously, then, if it is necessary to 
have single-phase instruments in the separate circuits, it is desirable 
to have them of the precision type, and polyphase instruments are not 
needed. 

RULES FOR CONDUCTING TESTS OF STEAM TURBINES 
AND TURBO-GENERATORS. A.S.M.E. CODE OF 1912 

Determine the object, take the dimensions, note the physical conditions 
not only of the turbine but of the entire plant concerned, examine 
for leakages, install the testing appliances, etc., as pointed out in the 
general instructions given on pages 258 to 263 and prepare for the test 
accordingly. 

The apparatus and instruments required for a simple performance test 
of a steam turbine or turbo-generator, in which the steam consumption 
is determined by feedwater measurement, are: 

(a) Tanks and platform scales for weighing water (or water meters calibrated in 

place). 
(&) Graduated scales attached to the water glasses of the boilers. 

(c) Pressure gages, vacuum gages, and thermometers. 

(d) A steam calorimeter. 

(e) A barometer. 

(J) A tachometer or other speed-measuring apparatus. 
(g) A friction brake or dynamometer. 

(h) Volt meters, ammeters, wattmeters, and watt-hour meters for the electrical 
measurements in the case of a turbo-generator. 

The determination of the heat and steam consumption of a turbine or 
turbo-generator should conform to the same methods as those described 
in the Steam Engine Code, pages 294 to 304. 

The steam consumed by steam-driven auxiliaries required for the 
operation of a turbine should be included in the total steam from which 
the heat consumption is calculated the same as in the case of the steam 
engine. 

Determine what the operating conditions should be to conform to the 
object in view and see that they prevail throughout the trial. 

The rules pertaining to the subjects Duration, Starting and Stopping, 
Records, and Calculation of Results, are identically the same as those 



326 POWER PLANT TESTING 

given under the respective headings in the Steam Engine Code, pages 
294 to 298 with the single exception of the matter relating to indicator 
diagrams and results computed therefrom; and reference may be made 
to that code for the directions required in these particulars. 

DATA AND RESULTS OF STEAM TURBINE OR TURBO-GENERATOR TESTS 

(1) Test of turbine located at 

to determine conducted by 

(2) Type of turbine and class of service 

(3) Type of generator, kind of current, etc 

(4) Rated power of turbine 

(5) Type of boiler 

(6) Kind and type of auxiliaries (air pumps, circulating pumps, feed pumps, 

etc.) 

(7) Dimensions of turbine or turbo-generator 

(8) Dimensions of boilers 

(9) Dimensions of auxiliaries 

(10) Dimensions of condenser 

(11) Date 

(12) Duration hrs. 

Average Pressures and Temperatures 

(13) Steam pipe pressure near throttle, by gage lbs. per sq. in. 

(13a) Absolute steam pipe pressure near throttle lbs. per sq. in # 

(14) Steam chest pressure by gage lbs. per sq. in. 

(14a) Absolute steam chest pressure lbs. per sq. in. 

(15) Barometric pressure of atmosphere in ins. mercury = lbs. per sq. in. 

(16) Vacuum in condenser: 

(a) In inches of mercury ins. 

(6) Corresponding absolute pressure lbs. per sq. in. 

(17) Exhaust chamber pressure (absolute) lbs. per sq. in. 

(17a) Temperature in steam pipe near throttle deg. F. 

(17b) Temperature in steam chest deg. F. 

(18) Temperature of main supply of feedwater to boilers . deg. F. 

(19) Temperature of additional supplies of feedwater deg. F. 

(20) Temperature of injection or circulating water entering condenser deg. F. 

(21) Temperature of injection or circulating water leaving condenser deg. F. 

Total Quantities 

(22) Water fed to boilers from main source of supply lbs. 

(23) Water fed from additional supplies lbs. 

(24) Total water fed to boilers from all sources lbs. 

(25) Moisture in steam or superheating near throttle per cent or deg. F. 

(26) Factor of correction for quality of steam, dry steam being unity 

(27) Total dry steam consumed for all purposes lbs. 

Hourly Quantities 

(28) Water fed from main source of supply lbs. 

(29) Water fed from additional supplies lbs. 



STEAM TURBINES AND TURBO-GENERATORS 327 

(30) Total water fed to boilers per hour lbs 

(31) Total dry steam consumed per hour lbs 

(32) Loss of steam and water per hour due to drips from main steam pipes and to 

leakage of plant lbs 

(33) Net dry steam consumed per hour lbs 

(34) Dry steam consumed per hour : 

(a) By turbine lbs 

(b) By auxiliaries lbs 

(35) Injection or circulating water supplied condensers per hour cu. ft 

Heat Data 

(36) Heat units per pound of dry steam, based on temperature of Line 18 B.t.u. 

(37) Heat units per pound of dry steam, based on temperature of Line 19 B.t.u. 

(38) Heat units consumed per hour, main supply of feed B.t.u. 

(39) Heat units consumed per hour, additional supplies of feed B.t.u. 

(40) Total heat units consumed per hour for all purposes B.t.u. 

(41) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. 

(42) Heat units consumed per hour: 

(a) By turbine and auxiliaries B.t.u. 

(b) By turbine alone B.t.u. 

(c) By auxiliaries B.t.u. 

Electrical Data 

(43) Average volts, each phase volts 

(44) Average amperes, each phase amperes 

(45) Average kilowatts, first meter kw. 

(46) Average kilowatts, second meter kw. 

(47) Total kilowatt output kw. 

(48) Power factor 

(49) Output consumed by exciter kw. 

(50) Net kilowatt output kw. 

Speed 

(51) Revolutions per minute 

(52) Variation of speed between no load and full load r.p.m. 

(53) Fluctuation of speed on suddenly changing from full load to no load, measured 

by the increase in the revolutions due to the change r.p.m. 

Power 

(54) Brake horse power b.h.p. 

(55) Electrical horse power e.h.p. 

Economy Results 

(56) Heat units consumed by turbine and auxiliaries per brake h.p.-hr B.t.u. 

(57) Dry steam consumed per brake h.p.-hr. : 

(a) By turbine and auxiliaries lbs. 

(b) By turbine alone lbs. 

(c) By auxiliaries lbs. 

(58) Dry steam consumed per kw.-hr. : 

(a) By turbine and auxiliaries lbs. 

(b) By turbine alone lbs. 

(c) By auxiliaries lbs. 



328 POWER PLANT TESTING 



Efficiency Results 



(59) Thermal efficiency ratio per brake horse power per cent 

(60) Ratio of economy of turbine to that of an ideal turbine working with the 

Rankine cycle 

Work Done per Heat Unit 

(61) Ft.-lbs. of net work per B.t.u. consumed by turbine and auxiliaries (1,980,000 

-=- Line 56) , , ft.-lbs. 



CHAPTER XIV 

METHODS OF CORRECTING STEAM TURBINE AND ENGINE TESTS TO 
STANDARD CONDITIONS 

Standard Conditions for Turbine and Engine Tests. If tests of steam 
turbines and engines could be always made at some standard vacuum, 
superheat and admission pressure, then turbines and engines of the 
same size and of the same type could be readily compared, and an engineer 
could determine without any calculations which of two turbines or 
engines was more economical for at least these standard conditions. But 
steam turbines and engines even of the same make are not often designed 
and operated at any standard conditions, so that a direct comparison of 
steam consumptions has usually no significance. 

It will be shown now how good comparisons of different tests can be 
made by a little calculation involving the reducing of the results obtained 
for varying conditions to assumed standard conditions. The method 
given here is that generally used by manufacturers for comparing different 
tests on the same turbine or engine (a " checking " process) or on different 
types to determine the relative performance. To illustrate the method 
by an application, a comparatively simple test will first be discussed. 

Practical Example. Corrections for Full-load Tests. The curve in 
Fig. 309 shows the steam consumption for varying loads obtained from 

















































35 


























































































Ho 

a* 35 

cs m 

20 










































































































































































































































































15 















































40 



1G0 



Fig. 309. 



80 100 120 140 
Output of Generator in Kilowatts 

Water Rate Curve of a Typical 125-Kilowatt Steam Turbine. 
Output.) 



(Generator 



tests of a 125-kilowatt steam turbine operating at 27.5 inches vacuum, 
50 degrees Fahrenheit superheat, and 175 pounds per square inch abso- 

329 



330 



POWER PLANT TESTING 



lute admission pressure (at the nozzles). It is desired to find the equiv- 
alent steam consumption at 28 inches vacuum, degrees Fahrenheit 
superheat, and 165 pounds per square inch absolute admission pressure 
for comparison with the " guarantee tests " (Fig. 310) of a steam engine 
of about the same capacity operating at the latter conditions of vacuum, 



53 





















































\ 

\ 
















































\ 








































35 


















































\B 




\ 


































































































^ 


























• 
























F^ 
















__ 


--" 






























































20 
































































A. Steam Consumption of Engine 










15 






















of Steam Turbine. 











60 80 100 120 140 

Output of Generator in Kilowatts 



Fig. 310. 



■ Comparative Water Rate Curves of a Reciprocating Steam Engine and a 
Steam Turbine. (Both with Standard Generators.) 

superheat and pressure. The manufacturers of the steam turbine have 
provided the curves in Figs. 311, 312, and 313, showing the change of 
economy with varying vacuum, superheat and pressure. With the help 
of these correction curves, the steam consumption of the turbine can be 






































































































































































































































































































































































2 





I 


1 






2 


J 


2 


4: 


2 


5 


2 


6 


2 


7 


2 


3 





) 





fl 30 

n 25 
O S 

Pi 
J320 



Vacuum Incnes of Mercury 
Fig. 311. — Vacuum Correction Curve for a 125-Kilowatt Steam Turbine. 

reduced to the conditions of the engine tests. Fig. 311 shows that 
between 27 and 28 inches vacuum a difference of 1 inch changes the steam 
consumption 1.0 pound. Fig. 312 shows a change of 2.0 pounds per 
100 degrees Fahrenheit superheat, and from Fig. 313 we observe a change 
of 5.0 pounds in the steam consumption for 100 pounds difference in 



CORRECTING STEAM TURBINE AND ENGINE TESTS 331 

admission pressure. Compared with the engine tests the steam turbine 
was operated at .5 inch lower vacuum, 50 degrees Fahrenheit higher 
superheat, and 10 pounds higher pressure. At the conditions of the 
engine tests, then, the steam consumption of the steam turbine should 
be reduced .5 pound to give the equivalent at 28 inches vacuum, but is 
increased 1.0 pound to correspond to degrees Fahrenheit superheat, and 

















































2h 














































20 


























































































15 


























































































10 

















































2 





i 





E 





i 




Sup 


1 
erh 


00 
3at- 


1 
Deg 


30 
s.F 


140 
ahr. 


160 


180 


200 





Fig. 312. — Superheat Correction Curve for a 125-Kilowatt Steam Turbine. 

.5 pound more to bring it to 165 pounds absolute admission pressure. 
The full-load steam consumption for the steam turbine at the conditions 
required for the comparison is, therefore, 24.5 — .5 + 1.0 + .5, or 25.5 
pounds. 1 

Persons who are not very familiar with the method of making these 
corrections will be likely to make mistakes by not knowing whether a 

















































.2 §25 
§M20 


















































































































































































I! 15 


























































































10 















































130 140 150 160 
Steam Pressure -Lbs. Per 



170 180 
. In. Abs. 



Fig. 313. — Pressure Correction Curve for a 125-Kilowatt Steam Turbine. 



correction is to be added or subtracted. A little thinking before writing 
down the result should, however, prevent such errors. When the per- 

1 The corrected steam consumption is found to be nearly the same as that which the 
three correction curves show for the same conditions, that is, about 25.0 pounds. If 
there had been a difference of more than about 5 per cent between the corrected steam 
consumption and that of the correction curves for the same conditions, the " ratio " 
method as explained on page 332 for fractional loads should have been used also for 
full load. 



332 POWER PLANT TESTING 

formance at a given vacuum is to be corrected to a condition of higher 
vacuum, the correction must be subtracted, because obviously the steam 
consumption is reduced by operating at a higher vacuum. When the 
steam consumption with superheated steam is to be determined in its 
equivalent of dry saturated steam (0 degrees superheat) the correction 
must be added because with lower superheat there is less heat energy in 
the steam and consequently there is a larger consumption. Usual correc- 
tions for differences in admission pressure are not large; but it is well 
established that the economy is improved by increasing the pressure. 

Corrections for Fractional Loads. It is the general experience of 
steam turbine manufacturers that full-load correction curves, if used by 
the following " ratio " or percentage method, can be used for correcting 
fractional or overloads. This statement applies at least without appreci- 
able error from half to one and a half load, and is the only practicable 
method for quarter load as well. 1 Stated in a few words, it is assumed 
then that the steam consumption at fractional loads is changed by the 
same percentage as at full load for an inch of vacuum, a degree of super- 
heat, or a pound pressure. It will now be shown how this method applies 
to the correction of the steam consumption of the turbine at fractional 
loads. Now according to the curve in Fig. 311, the steam consumption 
at 27.5 inches (25.6 pounds) must obviously be multiplied by the ratio 2 

25 

7^-3 , of which the numerator is the steam consumption at 28 inches and 

the denominator at 27.5 inches, to get the equivalent consumption at 
28 inches vacuum. This reasoning establishes the proper method for 
making corrections; that is, that the base for the percentage (denomina- 
tor of the fraction) must be the steam consumption at the condition to 
which the correction is to be applied. 3 Similarly the correction ratio to 
change the consumption at 50 degrees Fahrenheit superheat to degrees 

25.0 
Fahrenheit is ttt-f: , and to correct 175 pounds pressure to 165 pounds the 

24 8 
ratio is -^-^ . Data and calculated results obtained by this method may 

then be tabulated as follows: 

1 A very exhaustive investigation of this has been made by T. Stevens and H. M. 
Hobart, which is reported in Engineering, March 2, 1906. 

2 Assuming that this short length of the curve may be taken for a straight line with- 
out appreciable error. 

3 In nearly all books touching this subject so important to the practical, consulting, 
or sales engineer, the alternative method of taking the steam consumption at the re- 
quired conditions as the base for the percentage calculation is implied. By such a 
method percentage correction curves derived from straight lines like Figs. 208 and 209 
would be straight lines and, in application, give absurd results. Actually such per- 
centage corrections will fall on curves. 



CORRECTING STEAM TURBINE AND ENGINE TESTS 333 





Conditions 
of Test. 


Required 
Conditions. 


Correction 
Ratio. 


Percentage 
Correction. 




27.5 
50. 
175. 


28 



165 


25.0 
25.6 
25.0 
24.0 

24.8 
24.3 


-2.34%i 
+4.17% 
+2.06% 
+3.89% 




Admission pressure, pounds absolute 













25 
1 Steps in the calculations are omitted in the table, thus — — ■ = .9766 or 97.66 per 

25.6 

cent making the correction 100 — 97.66 or 2.34 per cent. It may seem unreasonable 
to the reader that these percentages are calculated to three figures when the third 
figure of the values of steam consumption is doubtful. In practice, however, the rul- 
ing of the curve sheets must be much finer and to larger scale so that the curves can 
be read more accurately. 

The signs +- and — are used in the percentage column to indicate 
whether the correction will increase or decrease the steam consumption. 
" Net correction " is the algebraic sum of the quantities in the last 
column. . 

The following table gives the results of applying the above " net cor- 
rection " to fractional loads. 





\ Load 
31.3 kw. 


J Load 
62.5 kw. 


jLoad 
93.8 kw. 


J Load 
125 kw. 


f Load 
156.3 kw. 


Steam consumption from test 
(Fig. 309) 


31.2 
+ 1.2 
32.4 


26.9 

+1.1 
28.0 


25.2 
+ 1.0 
26.2 


24.5 
+1.0 
25.5 


23.6 


Net correction + 3.89% 


+0.9 


Corrected steam consumption 


24.5 



Curve B in Fig. 310 shows the corrected curve of steam consumption 
for the steam turbine as plotted from the above table. By thus com- 
bining, on the same curve sheet, curves A and B as in this figure, the 
points of better economy of the turbine are readily understood. 

Results of economy tests of various turbines are of very little value for 
comparison when the steam consumptions or " water rates " are given for 
all sorts of conditions. With the assistance, however, of curves like those 
shown in Figs. 311, 312 and 313, if they are representative of the type and 
size of turbine tested, it is.possible to make valuable comparisons between 
two or more different turbines. Some very recent data of Curtis and 
Westinghouse-Parsons turbines are given below, together with suitable 
corrections adopted by the manufacturers for similar machines. 

The following test of a Westinghouse-Parsons turbine, rated at 7500 
kilowatts, was taken at Waterside Station No. 2 of the New York Edison 



334 



POWER PLANT TESTING 



7500-KILOWATT WESTINGHOUSE-PARSONS TURBINE, WATER-SIDE 
STATION NO. 2; NEW YORK EDISON COMPANY 







Corrected 
to 


Correction 
per cent. 1 




8 
750 
177.5 
27.3 
95.7 
9830.5 
15. 15 2 












Average steam pressure, pounds gage 

Average vacuum, ins. (referred to 30 in. barom.) 


179 
28.5 
100 


-0.15 
-3.36 
-0.29 


Average load on generator, kilowatts 












-3.80 


Corrected steam consumption, pounds per kilowatt- 




14.57 











1 The following corrections were given by the manufacturers and accepted by the 
purchaser as representative of this type and size of turbine: 

Pressure correction .1 per cent for 1 pound. 
Vacuum correction 3.5 per cent for 1 inch. 
Superheat correction 7.0 per cent for 100 degrees Fah- 
renheit. 

2 This is 7| per cent better than the manufacturer's guarantee. 



from Electric Journal, 
November, 1907, page 658. 



9000-KILOWATT CURTIS TURBINE, FISK STREET STATION, COM- 
MONWEALTH ELECTRIC COMPANY, CHICAGO 







Corrected 
to 


Correction 
per cent. 1 












750 
179 

29.55 
116 
8070 

13.0 








179 

28.5 
100 


.0 


Average vacuum, inches (referred to 30 in. barom.). . 


+ 12.39 
-j- 1.28 






Steam consumption, pounds per kilowatt-hour 








+13.67 


Corrected steam consumption, pounds per kilowatt- 




14.77 











1 The following percentage corrections were used: 
Superheat corrections 8 per cent for 100 degrees Fahrenheit. 



Vacuum correction 8 per cent for 1 inch from curve in Fig. 314. f 
Pressure correction hot given. J 



G. E. Bulletin, 
No. 4531. 



Co., and a comparison is made with a test of a five-stage 9000-kilowatt 
Curtis turbine at the Fisk Street Station of the Commonwealth Electric 
Company of Chicago. As no pressure correction is given for the Curtis 
machine, the New York Edison test is corrected to the pressure at which 
the other machine was operated (179 pounds per square inch gage). 
Approximately an average vacuum for the two tests is taken for the 



CORRECTING STEAM TURBINE AND ENGINE TESTS 335 



standard, and 100 degrees Fahrenheit superheat is used for comparing 
the superheats. These assumed standard conditions make the corrections 
for each turbine comparatively small. When two tests are to be com- 
pared, by far the more intelligent results are obtained if each is cor- 
rected to the average conditions of the two tests, rather than correcting 
one test to the conditions of the other. There is always a chance for 
various errors when large corrections must be made. 

These results show a difference of only .20 pound in the corrected 
steam consumption, so that for exactly the same conditions these two 
machines would probably give approximately the same economy. Each 
turbine is doubtless best for the special conditions for which it was 
designed. 

These results are equivalent to respectively 9.58 pounds and 9.72 
pounds per indicated horse power, assuming 97 per cent as the efficiency 
of the generator and 91 per cent as the mechanical efficiency of a large 
Corliss engine according to figures given by Scott. 1 

From experience with other similar turbines it seems as if the vacuum 
corrections given are too low for each turbine. The correction for the 

Curtis turbine was obtained „ 

from the curve in Fig. 314, 
as given between 27 and 28 
inches, while it was used be- 
tween 28.5 and 29.5 inches, 
where the curve of steam 
consumption most likely 
slopes somewhat as shown 
by the dotted line in the fig- 
ure, which was derived from 
the percentage change of the 
theoretical steam consump- 
tion calculated from the 
available energy. The cor- 
rection of 2.7 per cent per 

inch of vacuum for the Westinghouse-Parsons turbine is probably too 
low also, although the percentage correction would not be nearly as 
large as for the Curtis. If both of these corrections are too low, the 
effect of increasing them would be to increase the corrected steam con- 
sumption of the Curtis turbine and reduce that of the Westinghouse- 
Parsons. 

1 Electric Journal, July, 1907. It is stated also, in this article that the vacuum 
correction of a Westinghouse-Parsons turbine is 3.5 per cent per inch between 28 and 
28.5 inches. Jude states that the vacuum correction for Parsons turbines is 5 to 6 
per cent per inch. 



































































































































































V 






























s 






























\ 





























































23 24 25 26 27 28 29 

Vacuum Inches of Mercury 

Fig. 314. — Typical Vacuum Correction Curve 
for a 5000-Kilowatt Impulse Turbine. 



CHAPTER XV 

TESTS OF COMPLETE STEAM POWER PLANTS 
A. S. M. E. Code of 1912. 

These rules are intended to apply to commercial tests of a complete 
plant to determine the number of pounds of fuel consumed per unit 
of work done in a unit of time. For tests of the component parts of 
a complete plant, such as boilers, engines, turbines, etc., rules may- 
be found in the respective Codes on the preceding pages applying to 
such cases. 

Read the general instructions given on pages 258 to 263. Take the 
dimensions, note the physical conditions, examine for leakages, install 
the testing appliances, etc., as there pointed out, and prepare for the 
test accordingly. 

Fuel. Determine the character of the fuel to be used according to 
the object in view. For further particulars reference may be made to 
the Boiler Code, page 269. 

Apparatus and Instruments. The apparatus and instruments re- 
quired for a simple performance test of a steam plant are : 

(a) Platform scales for weighing coal and ashes. 

(b) Coal calorimeter. 

(c) Steam engine indicators. 

(d) A speed-measuring apparatus. 

(e) Electrical instruments for determining the output of an electric plant. 

If the test involves the determination of boiler performance, and 
engine or turbine performances, additional instruments should be used 
as pointed out in the respective Codes referring to such tests. 

Duration. The duration of a plant test should be not less than one 
day of 24 hours, and preferably a full week of seven days, including 
Sunday. 

In cases where the engine or turbine is in operation only a part of 
the day, the duration on which the results are computed should be 
considered the length of time that the engine or turbine is in opera- 
tion at its working speed. 

Starting and Stopping. In a plant operating continuously, day and 
night, the times fixed for starting and stopping should follow the regular 
periods of cleaning the fires. The fires should be quickly cleaned and 

336 



TESTS OF COMPLETE STEAM POWER PLANTS 337 

then burned low, say to a thickness of 4 inches. When this condition is 
reached the time should be noted as the starting time, and the thickness 
of each coal bed observed, as also the water levels and the steam pressure. 
Fresh coal should then be fired from that weighed for the test, the ashpits 
thoroughly cleaned, and the regular work of the test proceeded with. 
At the close of the test, following a regular cleaning, the fires should 
again be burned low, and when their condition has become the same as 
that observed at the beginning, the water levels and steam pressure also 
being the same, the time is observed and this time taken as the stopping 
time. If the water levels and steam pressure are not the same as at the 
beginning a suitable correction should be made by computation. The 
ashes and refuse are then hauled from the ashpits. 

In a plant running only a part of the day, and during the remainder of 
the day the fires are banked, the time selected for the beginning and 
end of the test should be that following the close of the day's run, when 
the fires have been burned low preparatory to cleaning and banking. 
The amount of live coal left on the grates under these circumstances is 
estimated at the beginning of the test, and the fires brought to the same 
condition, as near as may be, at the close of the test the next day. If 
the two quantities differ, a suitable correction is made in the weight of 
coal fired, as found by calculation. 

Records. The general data should be recorded as pointed out on 
page 296, under the head of Records. Half-hourly readings of the 
various instruments concerned are usually sufficient, excepting where 
there are wide fluctuations. A set of indicator diagrams should be 
obtained at intervals of 20 minutes, and at more frequent intervals 
if the nature of the test makes it necessary. Mark on each card the 
cylinder and the end on which it was taken, also the time of the day. 
Record on one card of each set the readings of the pressure gages con- 
cerned, taken at the same time. These records should subsequently 
be entered on the general log, together with the areas, pressures, lengths, 
etc., measured from the diagrams, when these are worked up. 

Sampling and Drying Coal. During the progress of the test the 
coal should be regularly sampled for the purpose of analysis and deter- 
mination of moisture. 

Ashes and Refuse. The ashes and refuse withdrawn from the furnace 
and ashpit during the progress of the test and at its close should be 
weighed in a dry state, and, if desired, a representative sample should be 
obtained for proximate analysis and the determination of the amount 
of unburned carbon which it contains. 



338 POWER PLANT TESTING 



DATA AND RESULTS OF COMPLETE STEAM POWER PLANT TEST 

(1) Test of plant located at 

to determine conducted by 

(2) Type of engine or turbine and class of service 

( (3) Rated power of engine or turbine 

(4) Type of boilers 

(5) Kind and type of auxiliaries (air pump, circulating pump and feed pump; 

jackets, heaters, etc.) 

(6) Dimensions of engine or turbine 

(7) Dimensions of boilers 

(8) Dimensions of auxiliaries 

(9) Dimensions of condenser 

(10) Date 

(11) Duration hrs. 

(12) Length of time engine or turbine was in motion with throttle open hrs. 

(13) Length of time engine or turbine was running at normal speed hrs. 

(14) Kind of coal 

(15) Size of coal 

Average Pressures and Temperatures 

(16) Steam pressure at boiler by gage lbs. per sq. in. 

(17) Steam pipe pressure near throttle, by gage lbs. per sq. in. 

(18) Barometric pressure of atmosphere in in. of mercury 

(19) Pressure in receiver by gage lbs. per sq. in. 

(20) Vacuum in condenser ins- 

(20a) Temperature of steam near throttle deg. F. 

(21) Number of degrees of superheating, if any, near throttle deg. F. 

(22) Temperature of feedwater entering boilers deg. F. 

Total Quantities, Time, Etc. 

(23) Total coal as fired 1 lbs. 

(24) Moisture in coal per cent 

(25) Total dry coal consumed lbs. 

(26) Ash and refuse lbs. 

(27) Percentage of ash and refuse to dry coal per cent 

(28) Calorific value by calorimeter test per lb. of dry coal B.t.u. 

(29) Cost of coal per ton of lbs dollars 

Hourly Quantities 

(30) Dry coal consumed per hour, based on duration of running period ... .... lbs. 

Indicator Diagrams 

(31) Mean effective pressure in lbs. per sq. in 

Electrical Data 

(32) Total electrical output kw.-hr. 

(33) Electrical output per hour kw. 

1 Where an independent superheater is used, this includes coal burned in the super- 
heater. See also footnote page 277. 



TESTS OF COMPLETE STEAM POWER PLANTS 339 

(34) Output consumed by exciter kw. 

(35) Net electrical output per hour kw. 

(36) Average volts each phase volts 

(37) Average amperes each phase amperes 

(38) Power factor 

Speed 

(39) Revolutions per minute 

Power 

(40) Indicated horse power developed by main engine: 

First cylinder i.h.p. 

Second cylinder i.h.p. 

Whole engine i.h.p. 

(41) Net electrical horse power e.h.p. 

Economy Results 

(42) Dry coal consumed per i.h.p. per hour lbs. 

(43) Dry coal consumed per kw.-hr lbs. 

(44) Cost of coal per i.h.p. per hour cents 

(45) Cost of coal per kw.-hr '. cents 

" Plant " as used in this report should include the entire equipment of 
the steam plant producing power; that is, the main cylinder or cylinders, 
the steam jackets and reheaters, the air, circulating and boiler-feed 
pumps if steam driven, and any other machinery driven by steam re- 
quired for the operation of the engine. That the engine plant should be 
charged with the steam used by all the auxiliary machinery in determining 
the plant economy is necessary because the steam consumption of the 
engine is finally benefited, or at least it should be, by the heat they return 
to the system. It is, of course, now the general practice in commercially 
operated plants to pass the exhaust steam from auxiliaries operated non- 
condensing through a feedwater heater, thus carrying back to the boiler 
a great deal of the heat. 

When a plant is operating non-condensing, discharging the steam into 
the atmosphere, or with a jet condenser, the steam consumption of the 
engine cannot be determined by weighing or measuring the steam used 
as can be done when a surface condenser is used. The method followed 
in this case is to determine the steam used by the weight of water supplied 
to the boiler, assuming, of course, that all the steam from the boiler or 
boilers used goes to the engine tested. It can usually be arranged for a 
test of one of the engines in a large plant that one or more boilers can be 
segregated or cut off in the piping connections so that these boilers alone 
supply the engine. When, however, this method is to be used it is 
necessary to determine by a separate test the leakage of the boiler and of 
the piping from the boiler to the throttle valve of the engine. This leak- 



340 POWER PLANT TESTING 

age is, of course, the amount of feed-water pumped into the boiler to keep 
the level in the water gage constant without taking away any more steam 
than is lost in this way. When determining this leakage, the pressure in 
the boiler must be maintained the same as that at which steam is to be 
supplied to the engine for its test. The feed-water pumped into the boiler 
supplying the engine less the boiler and pipe leakage will be the net 
amount of steam used by the engine. 



CHAPTER XVI 

GAS AND OIL ENGINE AND PRODUCER TESTING 

The testing of internal combustion engines of the reciprocating type 
operating with gas, gasoline, kerosene, and alcohol does not differ essen- 
tially in the important details from steam engine practice already explained 
in Chapter XII. Indicator diagrams can be utilized to show the inner 
workings in the engine cylinder, giving a record of the pressure, " timing " 
of the valves and ignition for the operation of the engine through a cycle. 1 

Brake horse power is measured with a Prony brake or any other type 
of dynamometer permitting the determination with facility of the power 
of the engine. If with a Prony brake or similar device then the brake 
horse power is expressed by the usual formula 

b.h.p. = , (104) 

33)Ooo' v *' 

where 1 is the length of the brake-arm in feet, n is the number of revolu- 
tions per minute, and w is the net weight indicated by the scales on the 
brake. Similarly the indicated horse power is given by the usual formula 
for a single-acting steam engine (page 143) except that the number of 
explosions must be used in calculations instead of the number of revolu- 
tions, thus, 

. , plan e , . 

l.h.p. = -£ , (105) 

33>ooo' 

where p is the mean effective pressure in pounds per square inch measured 
from the indicator diagram, 1 is the length of the stroke in feet, a is the 
area of the piston in square inches, and n e is the number of explosions 
per minute, then 

Mechanical Efficiency = ^-^- (106) 

Certain important precautions should be observed when taking 
indicator diagrams, so that a reasonable degree of accuracy may be 
expected from the results of tests. In the first place the connections 

1 In what is called usually a four-cycle engine there are four piston strokes — one 
each for suction, compression, expansion, and exhaust, corresponding to two revolu- 
tions of the crank shaft for a complete cycle, while in a so-called two-cycle engine, two 
strokes of the piston make a complete cycle — corresponding to one revolution of the 
crank-shaft. In the latter case suction and compression are combined in one stroke 
and expansion and exhaust in another. 

341 



342 



POWER PLANT TESTING 



between the indicator and the combustion chamber should be as short 
as possible. It is much more important that in an internal-combustion 
engine the volume by which the combustion chamber (clearance) is 
increased by the indicator connections should be small in comparison to 
the volume of the engine cylinder than in a steam engine; because by 
increasing the clearance volume, obviously, the pressure resulting from 
compression is reduced as well as the pressure due to the explosion. It 
is in this way that large indicators and indicator connections may cause 




Fig. 315. — Crosby Gas Engine Indicator. 

a considerable reduction in the thermal efficiency of an engine, that is, 
reducing the efficiency of the transformation of heat energy into work. 

Tests of gas engines as made commercially have usually three objects 
in view: 

(1) Brake horse power. 

(2) Indicated horse power. 

(3) Gas or oil consumption per horse power per hour. 

Many types of gasoline engines, particularly those designed for the 
automobile service, operate at such high speeds that the indicated horse 
power cannot be obtained with accuracy. In many other kinds of en- 
gines classed in this group the mechanical efficiency is very low. It is 



GAS AND OIL ENGINE AND PRODUCER TESTING 343 

for these reasons that such engines are rated by the useful or brake horse 
power instead of by the indicated horse power, as with steam engines. 
Brake horse power is therefore the prime criterion by which the per- 
formance of these engines is expressed. 

Ordinary types of steam engine indicators, moreover, are not very 
satisfactory for testing gas engines, and many engineers prefer to use one 
of the type shown in the accompanying illustration, Fig. 315. It differs 
essentially from steam engine indicators of the same type in having in the 
lower part of the main " barrel," a cylinder of smaller diameter than the 
one just above it, containing the spring. This smaller cylinder takes a 
piston of only half the area of the standard size. By this means the scale 
of the spring ordinarily used is doubled and the shock on the small rods 
and levers of the pencil motion is only half as great, thus making the 
liability to breakage and the cost of repairs for such indicators very much 
less than when a piston of the standard size is used. 

Measurement of the Fuel Used. For tests of gas engines the gas used 
is usually measured by means of a gas meter. A so-called " wet " meter 
(page 177) is always to be preferred, but if a carefully calibrated dry 
meter is used very good results can be obtained and it is accurate enough 
for commercial tests. For gasoline, kerosene and other oil engines the 
amount of fuel used is preferably determined by direct weighing. The 
author has found the automatic indicating scales of the pendulum type 1 
now generally used by grocers and meat dealers to be most satisfactory. 
By this means the weight of the oil remaining in the " supply " vessel 
can be observed regularly throughout a test just as with a gas meter, so 
that irregularities in operation can be immediately observed. The 
vessel containing the oil used by the engine when placed on a scales must 
be connected to the carbureter or the pump, as the case may be, with a 
very flexible metallic tube made without rubber insertion. 2 If an indicat- 
ing scales is not available a very small platform or grocers' beam scales 
can be used satisfactorily, although if the weight of fuel oil is desired at 
regular intervals throughout a test some little time is required to balance 
the poise. 

Another method very commonly applied, however, is to use a cylindrical 
vessel of small diameter provided with a gage glass in which the level of 
the liquid can be observed. Such a vessel can be calibrated to determine 
the weight or volume of oil per inch of height measured on the gage 
glass. 

1 Very satisfactory scales for this purpose are made by the Toledo Scale Co., of 
Toledo, Ohio. Similar scales of the spring type are not recommended, because neces- 
sarily some of the vibrations of the engine will be transmitted to the scales and. the in- 
dications of the pointer will not be as accurate as they should be. 

2 Tubes of this kind are made by the Pennsylvania Flexible Metallic Tubing Co., 
Philadelphia. 



344 



POWER PLANT TESTING 



150: 

.140 



.9120 



8,110- 



Observations taken for a test of a gas or oil engine are in general much 
more uniform than the corresponding data taken in a steam engine trial. 

For this reason gas engine tests in 
particular can be made of much 
shorter duration than upon a steam 
engine for the same degree of accu- 
racy. 

For both gas and oil engines the 
points plotted on a scale of brake 
horse power for abscissas and fuel 
used per unit of time for ordinates 
will fall along a straight line, similar 
and resembling the Willans line for 
steam engines and steam turbines (see 
page 312). A typical set of curves 
of the results of a test of a gas engine 
is shown in Fig. 316. Brake horse 
power is taken for the abscissas, as 
should always be done for gas and oil 
engine tests and gas used per hour, to 
its corresponding scale of ordinates, 
is given by the top curve. Other 
curves show the gas used per brake 
horse power per hour and per indi- 
cated horse power per hour, the indi- 
cated horse power, the mechanical 
efficiency, the number of explosions 
per minute, the revolutions per minute and the thermal efficiency (heat 
equivalent of the brake horse power 1 divided by heat supplied). 

If the engine is one using gas generated from coal in a producer, the 
test should cover a long enough period of time to determine with accuracy 
the coal used in the gas producer ; such a test should be of at least twenty- 
four hours' duration, and in most cases it should preferably extend over 
several days. 

Gas bags should be placed between the meter and the engine to di- 
minish the variations of pressure, and these should be of a size propor- 
tionate to the quantity used. Where a meter is employed to measure 
the air used by an engine, a receiver with a flexible diaphragm should be 
placed between the engine and the meter. The temperature and pressure 
of the gas should be measured, as also the barometric pressure and tem- 
perature of the atmosphere. 

1 Most engineers consider the thermal efficiency calculated on the basis of brake 
horse power more important than that based on indicated power because, particularly 
for high-speed engines, indicators are not very reliable. 





j : 

:: ::z:: :::::: 
...zt ........ 




- tZZZZ-Z ----- -Z 


:EEE ztt~zz 

_L1U ^ 


: :: . cm 


TTT «/ 

|¥:::::?::::::::: 
±zW :::2 ::::::: :; 


?3h 

:fe:::!!:::i6 
''W. 


IWMllPfflip 

±±izz-"2iz z\M& 


|i 5 

jJJfiaijaflXj-- 

— r^-'&m 1 ----- 

Wf+- 4 


7T/T^ Z/ " 

Tif~-^\7 L Tllir 

^WJmtfflil 

■H "TV §f ":::: 

P flffp 

iipiSl 


V 3 

ual-Efi oiemW n 

1 

r-f 

:^^i s i:::: : 

ffiffPffl 



Fig. 316. — Typical Economy, Speed, 
Horse Power, and Efficiency Curves of 
a Five Horse Power Gas Engine. 



GAS AND OIL ENGINE AND PRODUCER TESTING 345 

RULES FOR CONDUCTING TESTS OF GAS AND OIL ENGINES. 
A.S.M.E. CODE OF 1912. 

Determine the object, take the dimensions, note the physical condition 
of the engine and its appurtenances, install the testing appliances, etc., as 
explained in the general instructions given on pages 258 to 263, and 
make preparations for the test accordingly. 

Apparatus and instruments required for simple performance tests of 
gas and oil engines are: 

(a) Tanks and platform scales for weighing oil. 

(b) A calorimeter for determining the heat of combustion of oil. 

(c) A gas meter or other apparatus for measuring gas. 

(d) A gas calorimeter. 

(e) Pressure gages and thermometers. 
(/) Gas engine indicators. 

(g) A planimeter. 

(h) A speed-measuring apparatus. 

(i) Gas analyzing apparatus. 

(j) Scales and tanks for weighing or a water meter for measuring jacket water. 

(k) A dynamometer. 

Duration. The test of a gas or oil engine with substantially constant 
load should be continued for such time as may be necessary to obtain a 
number of successive records covering periods of half an hour or less 
during which the results are found to be uniform. In such cases a 
duration of from three to five hours is sufficient for all practical purposes. 1 

Starting and Stopping. The engine having been set to work under the 
prescribed conditions and thoroughly heated (except in cases where the 
object is to obtain the performance under working conditions), the test 
is begun at a certain predetermined time by commencing to weigh the 
oil, or measure the gas, as the case may be, and take other data concerned; 
after which the regular measurements and observations are carried 
forward until the end. When the stopping time arrives the test is closed 
by simply taking the final readings. 

Calorific Tests and Analyses. The quality of the oil or gas should be 
determined by calorific tests and analyses made on representative 
samples. 

CALCULATION OF RESULTS 

(a) Heat Consumption. The number of heat units consumed by the engine is found 
by multiplying the heat units per lb. of oil or per cu. ft. of gas (higher value), 
as determined by calorimeter test, by the total weight of oil in lbs. or volume of 
gas in cu. ft. consumed during the trial. 

1 For tests of maximum power for high-speed engines, it is often impracticable to 
run tests for a total duration of more than an hour. — Author. 



346 POWER PLANT TESTING 

(b) Horse Power and Efficiency. The indicated horse power, brake horse power, 
and efficiency are computed by the same methods as those explained in the 
Steam Engine Code, on pages 296 to 298, to which reference may be made. 

(c) Heat Balance. The various quantities showing the distribution of heat in the 
heat balance given in Table 2, page 348, are computed in the following manner: 

The heat converted into work per i.h.p.-hr. (2545 B.t.u.) is found by dividing 
the work representing 1 h.p., or 1,980,000 ft.-lbs., per hour by the number of 
ft.-lbs. representing 1 B.t.u., or 778. 

The heat rejected in the cooling water is obtained by multiplying the weight 
of water supplied by the number of degrees rise of temperature, and dividing 
the product by the indicated horse power. 

The heat rejected in the dry exhaust gases per i.h.p.-hr. is found by multiply- 
ing the weight of these gases per i.h.p.-hr. by the sensible heat of the gas reckoned 
from the temperature of the air in the room and by its specific heat. The 
weight of the dry gases per i.h.p.-hr. may be found by multiplying the weight of 
dry gas per lb. of carbon, using the formula: 

11C0 2 + 8Q + 7(C0 + N) 

3 (C0 2 + CO) (I ° 7) 

in which C0 2 , CO, O, and N are expressed in percentages by volume, by the 
proportion borne by the carbon in the total fuel (either gas or oil), and by the 
weight of fuel per i.h.p.-hr. 

The heat lost in the moisture formed by the burning of hydrogen in the gas 
is found by multiplying the total heat of 1 lb. of superheated steam at the tem- 
perature of the gas, reckoning from the temperature of the air in the room, by 
the proportion of the hydrogen in the fuel as determined from the analysis, and 
multiplying the result by 9. 

The heat lost through incomplete combustion is obtained by analyzing the 
exhaust gases and computing the heat of the unburned products which would 
have been produced by their combustion. 



TABLE 1. DATA AND RESULTS OF GAS OR OIL ENGINE TEST — SHORT 
FORM. CODE OF 1912 

(1) Test of engine, located at 

to determine conducted by 

(2) Type and class of engine and number of cycles 

(3) Dimensions: 

(a) Single or double acting 

(6) Diameter of cylinders ins. 

(c) Stroke of pistons ft. 

(d) Diameter of piston rods ins. 

(e) Compression space or clearance per cent 

(/) H.p. constant for 1 lb. m.e.p. and 1 r.p.m 

(4) Rated capacity 

(5) Date 

(6) Duration hrs. 

(7) Kind of gas 

(8) Kind of oil 

(9) Physical properties of oil (specific gravity, burning point, and flashing point) 



GAS AND OIL ENGINE AND PRODUCER TESTING 347 



Average Pressures and Temperatures 

(10) Pressure of gas near meter ins. water 

(11) Barometric pressure ins. mercury = lbs. per sq. in. 

(12) Temperature of cooling water: 

(a) Inlet deg. F. 

(b) Outlet deg. F. 

(13) Temperature of gas near meter deg. F. 

(14) Temperature of air deg. F. 

(15) Temperature of exhaust gases deg. F. 

Total Quantities 

(16) Gas or oil consumed cu. ft. or lbs. 

(17) Cooling water supplied to jackets lbs. 

(18) Calorific value of gas per cu. ft., or of oil per lb., by calorimeter test (higher 

value) B.t.u. 

Hourly Quantities 

(19) Gas or oil consumed per hour cu. ft. or lbs. 

(20) Cooling water supplied to jackets per hour lbs. 

Indicator Diagrams 

(21) Maximum pressure lbs. per sq. in. 

(22) Mean effective pressure lbs. per sq. in. 

Speed and Explosions 

(23) Revolutions per minute 



(24) Average number of explosions per minute . 



Power 

(25) Indicated horse power i.h.p. 

(26) Brake horse power b.h.p. 

(27) Friction horse power by difference Line 25 — Line 26 fr. h.p. 

(28) Friction horse power by friction diagrams fr. h.p. 

(29) Percentage of indicated horse power lost in friction (Line 27) per cent 

Economy Results 

(30) Heat units consumed by engine per hour 1 : 

(a) Per indicated horse power B.t.u. 

(b) Per brake horse power B.t.u. 

(31) Pounds of oil or cubic feet of gas consumed per hour: 

(a) Per indicated horse power cu. ft. or lbs. 

(&) Per brake horse power cu. ft. or lbs. 

Sample Diagrams 

Note. For an engine driving an electric generator the form may be enlarged to in- 
clude electrical data in the manner given in the Steam Turbine Code, page 327. 

1 If these results in the case of a gas engine are based on the "lower value" of the 
heat units, that fact should be so stated. 



348 POWER PLANT TESTING 

TABLE 2. DATA AND RESULTS OF GAS OR OIL ENGINE TEST — COM- 
PLETE FORM. CODE OF 1912 

(1) Test of engine, located at 

to determine conducted by 

(2) Type of engine, whether oil or gas 

(3) Class of engine (mill, marine, motor for vehicle, pumping, or other) 

(4) Number of revolutions for one cycle, and class of cycle 

(5) Method of ignition 

(6) Name of builders 

(7) Dimensions: 

(a) Class of cylinder, whether working or compressing 

(b) Vertical or horizontal 

(c) Single or double acting 

(d) Diameter of cylinders ins. 

(e) Stroke of pistons ft. 

(/) Diameter of piston rods ins. 

(g) Compression space or clearance, . . cu. in = . . per cent of piston displacement 
(Ji) H.p. constant for 1 lb. m.e.p. and 1 r.p.m 

(8) Rated capacity 

(9) Date 

(10) Duration hrs. 

(11) Kind of oil 

(12) Physical properties of oil (specific gravity, burning point, flashing point) 

(13) Kind of gas 

Average Pressures and Temperatures 

(14) Pressure of gas near meter ins. water 

(15) Barometric pressure ins. mercury = lbs. per sq. in. 

(16) Temperature of cooling water: 

(a) Inlet deg. F. 

■(6) Outlet deg. F. 

(17) Temperature of gas near meter deg. F. 

(18) Temperature of air: 

(a) By dry-bulb thermometer deg. F. 

(b) By wet-bulb thermometer deg. F. 

(19) Temperature of exhaust gases deg. F. 

Total Quantities 

(20) Gas or oil consumed cu. ft. or lbs. 

(21) Air supplied in cu. ft cu. ft. 

(22) Cooling water supplied to jackets lbs. 

(23) Calorific value of oil per lb., or of gas per cu. ft., by calorimeter test (higher 

value) B.t.u. 

Hourly Quantities 

(24) Gas or oil consumed per hour cu. ft. or lbs. 

(25) Cooling water supplied per hour lbs. 



GAS AND OIL ENGINE AND PRODUCER TESTING 349 



Analysis of Oil 

(26) Carbon (C) per cent 

(27) Hydrogen (H) per cent 

(28) Oxygen (O) per cent 

(29) Sulphur (S) per cent 

(30) Moisture per cent 

100 per cent 
Analysis op Gas by Volume 

(31) Carbon dioxide (C0 2 ) per cent 

(32) Carbon monoxide (CO) per cent 

(33) Oxygen (O) '. per cent 

(34) Hydrogen (H) per cent 

(35) Marsh gas (CH 4 ) per cent 

(36) Olefiant gas (C 2 H 4 ) per cent 

(37) Nitrogen (N by difference) per cent 

100 per cent 
Indicator Diagrams 

(40) Pressure in lb. per sq. in. above atmosphere: 

(a) Maximum pressure lbs. per sq. in. 

(6) Pressure at beginning of stroke lbs. per sq. in. 

(c) Pressure at end of expansion lbs. per sq. in. 

(d) Exhaust pressure at lowest point lbs. per sq. in. 

(41) Mean effective pressure in lbs. per sq. in 

Speed and Explosions 

(42) Revolutions per minute 

(43) Average number of explosions per minute 

(44) Variation of speed between no load and full load r.p.m. 

(45) Fluctuation of speed on suddenly changing from full load to no load measured 

by the increase in the revolutions due to the change 

Power 

(46) Indicated horse power i.h.p- 

(47) Brake horse power b.h.p- 

(48) Friction horse power by difference (Line 46 = Line 47) fr. h.p. 

(49) Friction horse power by friction diagrams fr. h.p. 

(50) Percentage of indicated horse power lost in friction (Line 48) per cent 

Economy Results 

(51) Heat units consumed by engine per hour 1 : 

(a) Per indicated horse power B.t.u. 

(b) Per brake horse power B.t.u. 

(52) Pounds of oil or cubic feet of gas consumed per hour: 

(a) Per indicated horse power cu. f t. or lbs. 

(6) Per brake horse power cu. ft. or lbs. 

1 If these results, in the case of a gas engine, are based on the "lower" value op the 
heat units, that fact should be so stated. See page 224. 



350 POWER PLANT TESTING 

Efficiency 

(53) Thermal efficiency ratio: 

(a) Per indicated horse power per cent 

(6) Per brake horse power per cent 

Work Done Per Heat Unit 

(54) Ft.-lbs. of net work per B.t.u. consumed (1,980,000 -^ Line 516) ft.-lbs. 

Heat Balance Based on B.t.tj. per i.h.p. per Hour 

B.t.u. Per Cent 

(55) Heat converted into work " 2545 

(56) Heat rejected in cooling water 

(57) Heat rejected in the exhaust gases 

(58) Heat lost due to moisture formed by burning of hydrogen 

(59) Heat lost by incomplete combustion 

(60) Heat unaccounted for, including radiation 

(61) Total heat consumed per i.h.p. per hour, same as Line 51a 

Sample Diagrams 

Note. For an engine driving an electric generator, the form may be enlarged to 
include electrical data in the manner given in the Steam Turbine Code, page 327. 

Indicator Diagrams of the Suction Stroke of a Gas or Oil Engine. 

With the ordinary stiff spring used for measuring the horse power of gas 
and oil engines, very little information regarding the action of the valves 
during the suction stroke is obtainable from the indicator diagram. For 
this reason the events in the suction stroke must be obtained with a com- 
paratively light spring, which must be protected, however, from injury 
when subjected to the excessive pressure of the explosion stroke by 
inserting a suitable stop of some kind to prevent undue compression of 




Fig. 317. — "Light Spring" Indicator Diagram of a Gas Engine 



the spring. The device usually adopted is to slip a small brass tube over 
the piston rod of the indicator to act as a distance piece. Another 
method, also satisfactory, is to fit a short but very thin brass tube over 
the outside of the spring, but of such a diameter that it will pass easily 
inside the cylinder of the indicator and rest freely on the top of the piston. 
A " light-spring " diagram is shown in Fig. 317, which was taken from 
an engine giving an ordinary diagram like Fig. 318. In Fig. 317 the 
lower horizontal line is the atmospheric line and the upper horizontal line 



GAS AND OIL ENGINE AND PRODUCER TESTING 351 

is traced by the pencil of the indicator, during the compression and 
explosion strokes, showing the effect of the stop. The wavy line S shows 
the exhaust stroke, and the slightly curved line E is the suction. The 
diagram shows that there was a partial vacuum throughout the suction 
stroke and for a part of the exhaust stroke, the latter effect being due 
doubtless to the inertia of the gases in the exhaust pipe. 




Fig. 318. — Normal Indicator Diagram of a Gas Engine. 

In the three figures following very interesting indicator diagrams 
of gas engines due to Pullen are illustrated. Figs. 319 and 320 show 
explosions during the suction stroke, generally called explosions in the 
air pipe, for the reason that since the air valve is then open the explosion 
occurred probably in the air pipe. In Fig. 319 the effect of the explosion is 
shown in the indicator diagram by the hump near the atmospheric line near 
the middle of the stroke, while in Fig. 320 the explosion occurred near the 




Fig. 319. — Indicator Diagram of a Gas Engine Showing Explosion in Air Pipe. 

end of the stroke. Explosions in the air pipe are sometimes attributed to 
there being too weak a mixture (too little rich gas) in the cylinder, caus- 
ing very slow burning instead of a sharp explosion. Under these condi- 
tions combustion will not be complete at the end of the working stroke, 
and this slow burning goes on through the exhaust stroke. Then when 
the exhaust valve closes, some of this smouldering gas remains in the 
clearance space, which, when mixed with the new charge during the 



352 



POWER PLANT TESTING 



next suction stroke, forms a combustible mixture which is easily exploded. 
Explosions of this nature are generally spoken of as " back-firing." 
In Fig. 320 the explosion occurred near the end of the suction stroke at 
x, and the air valve has closed before the pressure has had time to fall 
to atmospheric. On this account the compression line c is much higher 
than it would be under normal conditions as shown by b. Since no 




Fig. 320. — Abnormal Gas Engine Diagrams. 

explosion takes place at the proper time, the curve d corresponding to the 
working stroke lies just below this abnormal compression line. 

No less interesting are the diagrams illustrated in Fig. 321, showing 
the effect of pre-ignition on the indicator diagram of a gas engine. Here 
in two of the diagrams shown the ignition occurred too early or before 
the end of the compression stroke. Under these conditions there is 




Fig. 321. 



Indicator Diagrams of a Gas Engine Illustrating the Effect of "Timing" 
(from Pre-ignition to Slow Burning). 



usually a heavy thumping noise in the engine cylinder, and the engine 
will not develop as much power as there would be if ignition were "timed" 
a little later. This effect may be caused in poorly designed engines by 
some small metal projection or web in the clearance space becoming 
hot enough to ignite the charge before the ignition device operates. 
On the other hand, the point of ignition may have been advanced too 
far by inexperienced persons. 



GAS AND OIL ENGINE AND PRODUCER TESTING 353 

Fuels for Gas and Oil Engines. The ordinary type of gas engine is 
generally operated with either illuminating gas or natural gas. Since, 
however, natural gas occurs only in limited areas its use is very much 
restricted. Blast-furnace gas is used in iron works for operating engines 
with the waste gases from the blast furnaces. The gas from coke- 
ovens, also a waste gas, is now being used to some extent in the gas 
engines of power plants in the coke regions. Of the various kinds of 
so-called fuel gases producer gas is for the average engineer by far the 
most important. Anthracite coal is more easily converted into pro- 
ducer gas than any other fuel, although bituminous coals are now also 
used. The apparatus used for generating producer gas is called in tech- 
nical language a producer. There are in common use two types of pro- 
ducers for converting solid fuel into a permanent fuel gas. In one type 
the air or the steam (or both together) that is required for the operation 
of the producer is forced under pressure, produced usually by a blower, 
through the bed of solid fuel. In the other type of producer the air and 
water are drawn through the bed of fuel either by the suction of the 
engine itself, or by the suction of an auxiliary " exhauster." Gas is made 
at a more or less uniform rate in a pressure producer while it operates 
and the gas is stored in tanks, generally of comparatively small capacity, 
from which it is drawn to meet the varying needs of the engine. A suc- 
tion producer operating without an auxiliary " exhauster " is not pro- 
vided with a storage tank, but the gas is generated at the rate demanded 
by the needs of the engine. 

Producer Gas. The most common method for making producer gas to 
be used in engines is to admit both air and steam (or water vapor) simulta- 
neously and continuously to the incandescent fuel bed. Another method is 
to burn the fuel for a time with air alone ; that is, without any steam, until 
the fuel bed becomes highly incandescent, and then shut off the supply 
of air and pass steam or water vapor into the fuel until its temperature 
becomes so low that very little gas is formed and the air must be used 
again with the steam supply shut off. The producer continues in opera- 
tion by alternating the admission of air and steam to the fuel bed. The 
former of these two methods is the one most generally used. 

Suction Gas Producer. Anthracite coal is the most satisfactory 
fuel for suction gas producers, some preferring " chestnut " size, while 
others get the most satisfactory operation with the " pea " size if the 
coal supplied is clean. A producer or generator for such fuel is illustrated 
in Fig. 322. 

Capacity and Efficiency of Gas Producers. The important result 
to be determined from tests of a gas producer is the ratio of the heat 
value of the gas produced (in B.t.u.) to the heat value in the same 
units of the fuel used and the mechanical or electrical energy required 



354 



POWER PLANT TESTING 



in producing the gas. The capacity or the rate at which gas can be 
produced is also important, since a high rate of gasification means lower 
initial costs of the plant. In reports of tests of gas producers it should 
be clearly stated whether the higher or the lower heat value of the gas has 
been used in the calculations. There is no accepted rule as to whether 
the higher or the lower heat value should be used in guarantees, so that 
the one to be used must be clearly stated. Probably the best method 
of stating guarantees is to give the amount (volume) of gas at a standard 
temperature and pressure and the heat value (higher or lower as preferred) 
per unit volume (usually a cubic foot) that a producer and its accessories 
will deliver from a stated weight of coal, of which the heat value per 




Fig. 322. — Suction Gas Producer and Engine 



pound is also given. Mechanical, electrical, or other energy received 
from outside sources must also be taken into account. In the speci- 
fications for guarantees it should be stated that the loss of unburned 
fuel in the ash is to be charged as fuel used by the producer. 



RULES FOR CONDUCTING TESTS OF GAS PRODUCERS. 
A.S.M.E. CODE OF 1912 

Object and Preparations 

Determine the object, take the dimensions, and note the physical 
condition of the producer and its appurtenances. 

Fuel. 1 Determine the character of the fuel to be used. If an untried 
fuel is selected and a test-producer is available, make a preliminary trial 
of the fuel in this apparatus and ascertain its working characteristics 
and the proper methods of handling it. 

1 This code is primarily intended for producers using coal. If other fuel such as 
wood or oil, is burned, the rules may be modified accordingly. 



GAS AND OIL ENGINE AND PRODUCER TESTING 355 

In tests of maximum efficiency and capacity of a producer for com- 
parison with other producers, the fuel should be some kind of coal which 
is commercially regarded as a standard for such use in the locality where 
the test is made. The coal selected for such tests should be the best of 
its class and free from unusual slag-forming impurities. 

Apparatus and Instruments. The apparatus and instruments re- 
quired for producer tests are: 

(a) Platform scales for weighing coal and ashes. 
(&) A coal calorimeter. 

(c) A gas calorimeter. 

(d) Gas analyzing apparatus and appliances for determining tar and soot. 

(e) A gas meter, pitot tube, or other suitable apparatus for measuring the gas out- 

put. 
(/) A manometer or pressure gage. 
(g ) Water meters for measuring feed and scrubber water, and steam meters for 

measuring steam used by the apparatus. 
(h) Thermometers. 

The location of the pitot tube, if used, should be in the delivery pipe 
at a point near the producer or just beyond the scrubber, or at both 
points, according to the use made of the gas, either for fuel or power, and 
other requirements. 

Duration. The duration of both efficiency and capacity tests of a 
producer, with the exceptions noted below, should be such that the total 
consumption of fuel is at least ten times the weight of the fuel contained 
in the producer when in normal operation, estimating this weight in the 
case of coal at 45 lb. per cu. ft. 

In cases like down-draft producers which require the fuel bed to be 
entirely removed and rebuilt at regular intervals, and in producers where 
a complete cleaning and renewal occurs before the total consumption 
above stipulated has been reached, the duration should be that of the 
regular commercial operating cycle, or the time elapsing between two 
successive renewals of the fuel bed. 

Starting and Stopping. The conditions regarding the temperature of 
the producer and its contents, and the quantity and quality of the latter, 
should be as nearly as possible the same at the end as at the beginning 
of the trial. To secure the desired equality of conditions, the starting 
and stopping should occur at times of regular cleanings, and they should 
be preceded for a period of not less than 10 hours by the same regular 
working conditions as those characterizing the test as a whole. The 
operations of starting and stopping should then be carried on as follows: 

(a) Up-draft Suction Producers. Remove the ash and clinkers from the grate and 
the lower part of the furnace space, taking care that the crust or closely-united 
layer which supports the coal above is not unduly disturbed. Then break open 
the crust and allow the mass to drop into the space left vacant. Introduce a 



356 POWER PLANT TESTING 

poker rod through the poke holes in the upper head and stir up the coal within, 
thereby causing it to settle and fill the remaining spaces. As a final step, quickly 
replenish the producer with coal, leaving the hopper level-full, take the time, 
and consider this the starting time. Then clean the ash pit, and thereafter 
proceed with the regular work of the test, using weighed coal. 

When the time arrives for bringing the trial to a close, the cleaning operations 
described above are repeated, ending with fining the hopper, taking the time, 
and considering this the stopping time; finally hauling the ashes and refuse 
from the ashpit. 

(b) Up-draft Pressure Producers. Remove the ashes until the top of the ash bed 
is lowered to the normal working point, say six inches above the blast-hood. 
Introduce the poker-rod and break down any bridge or crust that may have 
formed, at the same time closing up the channels that run through the fuel 
bed, thereby making the bed homogeneous. Then replenish the producer with 
coal, fill the hopper level-full, take the time, and consider this the starting time. 
Thereafter proceed with the regular work of the test, using weighed coal. 

When the time approaches for closing the test, the operations above described 
are repeated, ending with replenishing the producer and filling the hopper with 
weighed coal, taking the time, and considering this the stopping time. The 
ashes and refuse finally removed are to be dried before weighing, or a sample 
should be taken and the moisture, as determined therefrom, allowed for. 

(c) Down-draft Pressure Producer. Thoroughly clean the producer of its entire 
contents. Introduce a weighed supply of coke or coal, start the fire and build 
up the fuel bed to its working condition, using weighed coal. When this point 
is reached, take the time, and consider this the starting time. Thereafter pro- 
ceed with the regular work of the test. 

When the time approaches for closing the test, burn the fuel bed as low as 
practicable to prepare for cleaning, stop the exhauster, note the time, and con- 
sider this the stopping time. Then completely empty the producer, quench 
the fire remaining in the live coals, separate and weigh the coke and ash, and 
deduct the weight of the former from that of the coke as charged. Finally dry 
the ash and refuse, or take a sample and allow for the moisture determined 
therefrom. 

The directions pertaining to Records, Sampling and Drying Coal, 
Ashes and Refuse, Calorific Tests and Analyses of Coal, are practically 
the same as those given under the corresponding headings in the Boiler 
Code, pages 269 and 276. 

Calorific Tests and Analyses of Gas Output. The quality of the gas 
should be determined by calorific tests and analyses, continuous samples 
for this purpose being taken from the delivery pipe at a point near the 
producer and at other points as may be needed. 

The calorific test should be made with the Junker calorimeter, or its 
equivalent. Unless otherwise required the " higher value " should be 
employed in calculating the results of the test. For an approximate 
determination of the composition of the gas, a modified type of Orsat ap- 
paratus may be used, and for complete determinations, the Hempel ap- 
paratus or its equivalent. The frequency with which these determinations 
should be made depends on the uniformity of the output, but the inter- 



GAS AND OIL ENGINE AND PRODUCER TESTING 357 

vals, where practicable, should not be more than one-half hour, the time 
taken for collecting each sample being not less than one-half hour. 



CALCULATION OF RESULTS 

(a) Total Volume of Gas Delivered. The volume of gas (cu. ft.) found by pitot tube 
measurement is determined by multiplying the area of the delivery pipe in sq. ft. 
at the tube by the velocity of the gas in ft. per minute, and the product by the 
duration of the trial in minutes. The equivalent volume at atmospheric pressure 
(30 in. barometer) and temperature of 62 deg. Fahr. is obtained by the usual 
method of thermodynamics as explained on page 226. 
(6) Net Volume of Gas Delivered. The net volume of gas delivered is found by sub- 
tracting from the total volume the equivalent volume of gas required for fur- 
nishing steam drawn from an outside source, if any, or for furnishing power used 
for any purpose concerned in the operation of the producer and its auxiliaries. 

(c) Weight of Gas. The weight of dry gas delivered is found by multiplying the 
volume in cu. ft., reduced to 62 deg. and 30 in. barometer, given in Table 2, 
page 360, Line 21, by the weight per cu. ft. of gas given in Table 2, Line 77. 

The weight of the gas per cu. ft. is determined by multiplying the percentage 
of each component gas as found by analysis (see Lines 55 to 63, Table 2, page 
361) by its weight in lb. per cu. ft., at -62 deg. and 30 in., barometer as given in 
the following table, and dividing the sum of the products by 100. 

C0 2 0.1116 CH 4 0.0428 

CO 0.0736 Q>H 4 0.0737 

2 0.0842 S0 2 0.1638 

Ho 0.0053 H 2 S 0.0868 

N 2 0.0740 

(d) Moisture in Gas Leaving Producer. The percentage of moisture in the gas is 
found by passing a measured sample of the gas through a chloride of calcium 
tube and weighing the amount of moisture absorbed. 

(e) Percentage of Tar and Soot in Gas. The percentage of tar and soot is found by 
comparing the total weight determined, including that collected from the vari- 
ous tar drips with the total weight of dry fuel used. 

(/) Efficiency. The efficiency is the relation between the calorific value of the gas 
per lb. of fuel charged, or combustible burned, and the calorific value of 1 lb. of 
fuel or combustible. The former is ascertained by multiplying the B.t.u. per 
cu. ft. of gas as determined by the calorimeter test (higher value) by the cu. ft. 
of gas delivered, and dividing the product by the total weight of fuel charged 
or combustible burned. 

The "combustible burned" is determined by subtracting from the weight 
of coal charged the moisture in the coal and the ash and refuse, including un- 
burned coal which is withdrawn from the producer or ash-pit during the progress 
of the trial. The "combustible" used for determining the calorific value is the 
weight of the coal less the moisture and ash found by analysis. 

The efficiency of "conversion and cleaning" in the above calculation is found 
by using the total volume of gas delivered. The "efficiency of the plant" is 
found by using the net volume of gas delivered. 

(g) Heat Balance. The various quantities showing the distribution of heat in the 
heat balance given in Table 2, page 361, are computed in the following manner: 



358 POWER PLANT TESTING 

The heat contained in the dry gas is found by multiplying the cubic feet of 
gas at 62 deg. and 30 in. barometer per lb. of dry coal by the calorific value of 
1 cu. ft. of gas at 62 deg. and 30 in. barometer (higher value). 

The heat carried away by the scrubber is obtained by multiplying the weight 
of water fed to the scrubber by the number of degrees rise of temperature, and 
dividing the product by the total weight of dry coal consumed. 

The heat contained in the moisture leaving the producer is found by mul- 
tiplying the total weight of dry gas by the proportion of moisture in the gas 
leaving the producer and by the total heat of 1 lb. of superheated steam at the 
temperature of the gas leaving the producer reckoned from the temperature of 
the air in the room, and dividing the product by the weight of dry coal con- 
sumed. 

Chart. In trials having for an object the determination and exposition 
of the complete performance from beginning to end, the entire log of 
readings and data should be plotted on a chart and represented graphi- 
cally. (See Fig. 296, page 268.) 

TABLE 1. DATA AND RESULTS OF GAS PRODUCER TEST — SHORT FORM. 
CODE OF 1912 

(1) Test of producer located at . . : 

to determine conducted by 

(2) Type of producer 

(3) Rated capacity of producer 

(4) Date 

(5) Duration , hrs. 

(6) Kind of coal 1 and where mined 

(7) Size of coal 

Average Pressures, Temperatures, Etc. 

(8) Steam pressure in vaporizer by gage lbs. per sq. in. 

(9) Gas pressure in delivery main at point where gas is measured ins. water 

(10) Temperature of feedwater deg. F. 

(11) Temperature of gas in delivery main near producer deg. F. 

(12) Temperature of gas in delivery main at point where gas is measured deg. F. 

(13) Force of blast or draft in ashpit ins. water 

Total Quantities 

(14) Weight of coal as charged lbs. 

(15) Percentage of moisture in coal per cent 

(16) Total weight of dry coal consumed lbs. 

(17) Total ash and refuse lbs. 

(18) Percentage of ash and refuse in dry coal per cent 

(19) Total cu. ft. of gas as measured cu. ft. 

(20) Equivalent cu. ft. of gas at 62 deg. F. and 30 in. barometer cu. ft. 

(21) Net cu. ft. of gas at 62 deg. F. and 30 in. 2 barometer cu. ft. 

(22) Total water fed to vaporizer lbs. 

(23) Total water supplied to scrubber lbs. 

1 If other fuel than coal is used the lines may be changed to read accordingly. 

2 After deducting equivalent gas required for auxiliaries. 



GAS AND OIL ENGINE AND PRODUCER TESTING 359 

Hourly Quantities 

(24) Dry coal consumed per hour lbs. 

(25) Dry coal per sq. ft. of main fuel bed per hour lbs. 

(26) Total cu. ft. of gas delivered per hour cu. ft. 

(27) Total cu. ft. of gas per hour at 62 deg. F. and 30 in. barometer cu. ft. 

(28) Net cu. ft. of gas per hour at 62 deg. F. and 30 in. barometer cu. ft. 

Economy Results 

(29) Total cu. ft. of gas delivered per lb. of dry coal (Line 13 -5- Line 10) cu. ft. 

(30) Equivalent total gas at 62 deg. F. and 30 in. barometer per lb. of dry coal. .cu. ft. 

(31) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of dry coal 1 . . . .cu. ft. 

(32) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of combustible. cu. ft. 

Efficiency 2 

(33) Calorific value of dry coal per lb B.t.u. 

(34) Calorific value of combustible per lb B.t.u. 

(35) Calorific value of gas per cu. ft. (higher value) B.t.u. 

(36) Efficiency of producer based on coal per cent 

(37) Efficiency of producer based on combustible per cent 

Cost of Production 

(38) Cost of coal per ton of .... lbs. delivered dollars 

(39) Cost of coal required for producing 10,000 net cu. ft. of gas at 02 deg. F. 

and 30 in. barometer dollars 

(40) Cost of coal required for producing one million B.t.u. in the gas dollars 

TABLE 2. DATA AND RESULTS OF GAS PRODUCER TEST — COMPLETE 
FORM. CODE OF 1912 

(1) Test of producer located at 

to determine conducted by 



Dimensions 

(2) Outside diameter of producer ft. 

(3) Height of producer ft. 

(4) Inside diameter of producer ft. 

(5) Diameter of grate ft. 

(6) Area of grate sq. ft. 

(7) Percentage of air space in grate per cent 

(8) Area of fuel bed (at maximum diameter) sq. ft. 

(9) Area of water-heating surface in vaporizer sq. ft. 

(10) Rated capacity of producer in lbs. of coal per hour lbs. 

(11) Date 

(12) Duration hrs. 

(13) Kind of coal 3 and where mined 

(14) Size of coal 

1 After deducting equivalent gas required for auxiliaries. 

2 If the efficiency is based on the "lower value" of the heat units in the gas the fact 
should be so stated. 

3 If other fuel than coal is used the lines may be changed to read accordingly. 



360 POWER PLANT TESTING 

Average Pressures, Temperatures, Etc. 

(15) Steam pressure in vaporizer by gage lbs. per sq. in. 

(16) Gas pressure in main at point where gas is measured ins. water 

(17) Force of blast or draft in ashpit ins. water 

(18) Barometric pressure . ins. mercury 

(19) Temperature of feedwater entering vaporizer deg. F. 

(20) Temperature of gas in main near producer deg. F. 

(21) Temperature of gas in main at point where gas is measured deg. F. 

(22) Temperature of air in room deg. F. 

(23) Temperature of water entering scrubber deg. F. 

(24) Temperature of water leaving scrubber deg. F. 

(25) Weight of dry gas per cu. ft. reduced to 62 deg. F. and 30 in. barometer lbs. 

Total Quantities 

(26) Weight of coal as fired lbs. 

(27) Percentage of moisture in coal per cent 

(28) Total weight of dry coal consumed lbs. 

(29) Total ash and refuse lbs. 

(30) Percentage of ash and refuse in dry coal per cent 

(31) Total number of cu. ft. of gas as measured cu. ft. 

(32) Equivalent cu. ft. of gas at temperature of 62 deg. F. and pressure of atmos- 

phere of 30 in. barometer cu. ft. 

(33) Net cu. ft. of gas at 62 deg. F. and 30 in. 1 barometer cu. ft. 

(34) Total weight of dry gas lbs. 

(35) Percentage of moisture in gas leaving producer per cent 

(36) Percentage of tar and soot in gas referred to total fuel per cent 

(37) Total water fed to vaporizer : lbs. 

(38) Total water evaporated in vaporizer lbs. 

(39) Total weight of steam supplied to producer lbs. 

(40) Total weight of water fed to scrubber lbs. 

Hourly Quantities 

(41) Dry coal consumed per hour lbs. 

(42) Dry coal consumed per hour per sq. ft. of grate lbs. 

(43) Dry coal consumed per hour per sq. ft. of main fuel bed lbs. 

(44) Total cu. ft. of gas delivered per hour (Line 20 -f- Line 17) cu. ft. 

(45) Total cu. ft. of gas per hour at 62 deg. F. and 30 in. barometer cu. ft. 

(46) Net cu. ft. of gas delivered per hour at 62 deg. F. and 30 in. barometer. . . .cu. ft. 

(47) Weight of dry gas per hour lbs. 

(48) Water fed per hour to vaporizer lbs. 

(49) Water evaporated per hour in vaporizer lbs. 

(50) Steam supplied to producer per hour lbs. 

(51) Water fed to scrubber per hour •. .lbs. 

Proximate Analysis of Coal 

(52) Fixed carbon per cent 

(53) Volatile matter per cent 

1 After deducting equivalent gas required for auxiliaries. 



GAS AND OIL ENGINE AND PRODUCER TESTING 361 

(54) Moisture per cent 

(55) Ash per cent 

100 per cent 

(56) Sulphur, separately determined per cent 

Ultimate Analysis op Dry Coal 

(57) Carbon (C) per cent 

(58) Hydrogen (H 2 ) per cent 

(59) Oxygen (0 2 ) per cent 

(60) Nitrogen (N 2 ) per cent 

(61) Sulphur (S) per cent 

(62) Ash per cent 

100 per cent 

(63) Moisture in sample of coal as received per cent 

Analysis op Ash and Refuse 

(64) Carbon per cent 

(65) Earthy matter per cent 

Analysis op Gas by Volume 1 

(66) Carbon dioxide (C0 2 ) per cent 

(67) Carbon monoxide (CO) per cent 

(68) Oxygen (0 2 ) per cent 

(69) Hydrogen (H 2 ) per cent 

(70) Marsh gas (CH 2 ) per cent 

(71) Olefiant gas (C 2 H 4 ) per cent 

(72) Sulphur dioxide (S0 2 ) per cent 

(73) Hydrogen sulphide (H 2 S) per cent 

(74) Nitrogen (N 2 by difference) per cent 

100 per cent 
Calorific Values by Calorimeter 

(75) Calorific value of dry coal per lb B.t.u. 

(76) Calorific value of combustible per lb B.t.u. 

(77) Calorific value of gas per cu. ft. at 62 deg. F. and 30 in. barometer (higher 

value) B.t.u. 

Economy Results 

(78) Total cu. ft. of gas as measured, per pound of dry coal consumed cu. ft. 

(79) Equivalent cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of dry coal . cu. ft. 

(80) Equivalent cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of com- 

bustible cu. ft. 

(81) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of dry coal. . . . cu. ft. 

(82) Net cu. ft. of gas at 62 deg. F. and 30 in. barometer per lb. of combustible, .cu. ft. 

1 Sample of gases should be collected at producer outlet before the gases pass through 
the scrubber as some of the carbon dioxide and hydrocarbons are absorbed in the 
scrubbers. 



362 POWER PLANT TESTING 



Efficiency 1 



(83) Efficiency of producer based on coal: 

(a) Conversion and cleaning per cent 

(6) Plant per cent 

(84) Efficiency of producer based on combustible: 

(a) Conversion and cleaning per cent 

(b) Plant per cent 

Cost of Production 

(85) Cost of coal per ton of ... . lbs., delivered dollars 

(86) Cost of coal required for producing 10,000 net cu. ft. of gas at 62 deg. F. and 

30 in. barometer .• dollars 

(87) Cost of coal for producing 1,000,000 B.t.u dollars 

Heat Balance Based on 1 Lb. of Dry Coal 

B.t.u. Per cent 

(88) Heat contained in dry gas 

(89) Heat carried away by scrubber 

(90) Heat contained in moisture leaving producer 

(91) Heat unaccounted for, including radiation, — difference be- 

tween the sum of Lines 88, 89, and 90 and Line 92 

(92) Total calorific value of 1 lb. of dry coal, same as Line 75 

RULES FOR CONDUCTING TESTS OF COMPLETE GAS 
POWER PLANTS. A.S.M.E. CODE OF 1912 

Object and preparations 

The usual object of testing a complete gas power plant, embracing 
producer, engine, and appurtenances, is the determination of its com- 
mercial performance, i.e., the number of pounds of fuel consumed per unit 
of work done in a unit of time, and the rules given in this code apply to 
tests having that object. For directions pertaining to tests of the 
producer and engine individually, reference may be made to the Producer 
and Gas Engine Codes, pages 345 and 354. Determine the character 
of the fuel to be used. 

The duration of a gas producer plant test should conform to that of 
the producer alone, rules pertaining to'which may be found in the Gas 
Producer Code. 

In cases where the engine is in operation only a part of the day, the 
hourly consumption of coal from which the economy results are com- 
puted should be the total coal burned in the producer divided by the 
number of hours that the engine is in operation at its working speed. 

The rules for starting and stopping a complete plant test are governed 
by those required for starting and stopping the test of the producer, 
which are those given in the Producer Code, page 355. 

1 If the efficiency is based on the "lower value" of the heat units in the gas, the fact 
should be so stated. 



GAS AND OIL ENGINE AND PRODUCER TESTING 363 

DATA AND RESULTS OF TEST OF COMPLETE GAS POWER PLANT. 
CODE OF 1912 

(1) Test of gas power plant at 

to determine conducted by 

(2) Type and dimensions of producers 

(3) Rated capacity of producers 

(4) Total area of main fuel bed at maximum diameter sq. ft. 

(5) Type and dimensions of engine 

(6) Rated power of engine 

(7) Date 

(8) Duration hrs. 

(9) Kind of coal 

(10) Size of coal 

Average Pressures and Temperatures 

(11) Pressure of gas near throttle valve ins. water 

(12) Barometric pressure ins. water 

(13) Temperature of cooling water leaving engine deg. F. 

(14) Temperature of air in room deg. F. 

Total Quantities 

(15) Weight of coal as charged lbs. 

(16) Percentage of moisture in coal per cent 

(17) Total weight of dry coal consumed lbs. 

(18) Total ash and refuse lbs. 

(19) Percentage of ash and refuse in dry coal per cent 

(20) Calorific value of 1 lb. of dry coal by calorimeter test B.t.u. 

(21) Cost of coal per ton of .... lbs dollars 

Hourly Quantities 

(22) Dry coal consumed per hour lbs. 

(23) Dry coal per sq. ft. of main fuel bed per hour lbs. 

Indicator Diagrams 

(24) Mean effective pressure in lbs. per sq. in 

Speed and Explosions 

(25) Revolutions per minute 



(26) Number of explosions per minute 

Power 

(27) Indicated horse power developed by engine i.h.p. 

Economy Results 

(28) Dry coal consumed per i.h.p. per hour lbs. 

(29) Cost of coal per i.h.p. per hour dollars 

(30) Heat units consumed per i.h.p. per hour (Line 20 X Line 28) B.t.u. 

Note. For an engine driving an electric generator, the form may be enlarged to 
include electrical data in the manner given in the code for Complete Steam Power 
Plants, page 336. 



CHAPTER XVII 

TESTING OF VENTILATING FANS OR BLOWERS AND AIR COMPRESSORS 

Centrifugal Fans are used almost exclusively when large volumes of 
air are to be handled at a comparatively small pressure. Such a fan 
consists essentially of a number of plates, either flat or curved, attached 
to radial arms springing from a central hub through which the driving 
shaft passes, as in the " spider " type shown in Fig. 325, or the blades 
may be attached to a conical plate as in Fig. 326. Fans resembling either 
of these two designs are known commercially as the " standard " type. 
The " width " of the blades is, in most cases, parallel to the shaft. 





Fig. 325. Fig 

"Standard" Types of Ventilating Fans. 

The work performed by a centrifugal type of fan is equal to the resist- 
ance times the velocity of flow. Since, however, the fan resistances are 
proportional to the square of the velocity, 1 the work done is proportional 
to the cube of the velocity. 

Disk or Propeller Fans are best illustrated by the so-called " electric " 
fans so commonly used in offices, shops and dwellings. Fans of this 
type are usually of a very light construction with the vanes arranged 
as in a screw propeller for a ship. In many cases fans of this type are 
not provided with casings, so that it is more difficult to make velocity 
measurements than with centrifugal fans. 

Turbine or " Sirocco " fans have an impeller or fan wheel of the 
" squirrel-cage " type, as illustrated in Fig. 327. Fans of this type 
can be designed to give very high efficiencies. This is due primarily 
to two characteristic features adopted in these designs. By the use 

1 See Professor Rateau's articles in Revue de Mecanique vol. 1, pages 629-837. 

364 



TESTING OF VENTILATING FANS OR BLOWERS 365 



of very short blades a very large intake space for the suction is pro- 
vided which is practically unobstructed, thus giving a very free " suction." 
The other important feature of this fan is that the air leaves the blades 
at a higher velocity than that at which the tips of the blades are moving. 
The importance of this re- 
sult is shown by a compari- 
son of Figs. 328 and 329. 
The former illustrates the 
type of blading in a turbine 
or " Sirocco " fan and shows 
graphically by a velocity 
diagram, constructed like a 
parallelogram of forces, the 
velocity of the tips of the 
blades V&, the velocity of 
radial flow in the blades V r 
and the absolute velocity of 
the discharge V a , which is 
the velocity of the air with 
respect to the stationary 
casing. It will be observed FlG . 327. — Turbine Type (Sirocco) Fan. 

that in Fig. 328, V a is nearly 

50 per cent greater than the velocity of the tips V & , while in Fig. 329, 
representing the corresponding velocities for a standard type of fan, the 






Fig. 328. — Velocity Diagram for a 
Turbine Fan. 



Fig. 329. — Velocity Diagram 
for a "Standard" Fan. 



absolute velocity of the discharge V a is actually considerably less than the 
speed of the tips of the blades. Increased velocity is accomplished in a 
type of fan like Fig. 328, not only by the curvature of the tips of the 
blades but also to some extent by making the blades somewhat concave 



366 



POWER PLANT TESTING 




Fig. 330. — Typical Positive Pressure Blower. 



with the inner ends (toward the center) practically radial. By this 
method of designing the outer edges of the blades have a smaller space 
between them than the inner edges. This has the effect of reducing the 
area on the discharge side of the blades and consequently the velocity of 
the air is increased. 

Positive Pressure Blowers are used principally for blast furnaces 
and smelters where a higher pressure is needed than can be efficiently 

obtained with a centrifugal fan. 
A section showing the rotors and 
casing of one of the blowers is 
shown in Fig. 330. It is often 
called Boot's blower. The effi- 
ciency of a blower of this type 
depends on the accuracy of the 
fitting of the two rotors, A and 
B, both with respect to each 
other and to the casing. It is 
for this reason that when new 
the efficiency is high, but after 
being in service for several years 
the bearings and the surfaces of 
the rotors will become worn, so 
that there is considerable leakage and consequent loss of efficiency. 

Tests of Ventilating Fans or Blowers are made usually by a very 
simple method; that is, by determining the necessary data for calcu- 
lating efficiency by measuring the work done by the fan " on the air " 
in giving velocity, and the power required to drive the fan alone, ex- 
cluding bearing friction. The fan is preferably operated by an electric 
motor, of which the efficiency can be readily determined by a Prony 
brake test. The power required to overcome the bearing friction of the 
shaft of the fan may well be first determined by measuring the power 
input 1 (kilowatts) for a series of speeds when the keys fastening the 
fan to its shaft have been removed and the fan itself has been " blocked " 
in its casing or, still better, has been removed from the shaft. After 
attaching the fan again to the shaft the input to the motor and the 
work done by the fan " on the air" should be determined for various 
speeds. Then obviously the ratio of the work done by the fan divided 
by the power required to drive it after correction for the efficiency 2 of 
the motor and bearing friction is the actual efficiency of the fan. In 
general terms this may be stated as follows : 

1 For normal operation "friction work" is, for machinery in general, proportional 
to the speed. 

2 Motor efficiency must be necessarily determined for the conditions of each test; 
that is, for the same kilowatts and speed as for each test. 



TESTING OF VENTILATING FANS OR BLOWERS 367 

f = input to motor to drive motor and shaft of fan in bearings, 

kilowatts ; 
i = input to motor to drive motor and fan, in kilowatts; 
e = efficiency of motor for motor input of i kilowatts and at 

speed of test; 
e' = efficiency of motor for motor input of f kilowatts and at speed 

of test. 

Then if i n is the net work in horse power to drive fan alone, 

i„ = z~ ' (108) 

0.746 ^ 

If the fan to be tested is direct-connected to a steam engine, the test 

is usually made by measuring the indicated horse power of the engine 

at the various speeds and also with the fan disconnected for no load. 

If it is possible to do so the fan should be removed from the shaft for 

the no-load test to determine bearing friction. ■ 

The work done by the fan " on the air" is most readily calculated 

by the same method used to calculate the efficiency of hydraulic pumps 

(see page 408), that is, by multiplying the number of pounds of air 

delivered per unit of time by the head in feet of air corresponding to the 

discharge pressure. This product is obviously in terms of work in 

foot-pounds per unit of time, and dividing by 33,000 the corresponding 

horse power is obtained. Using the following symbols, the same results 

may be expressed, however, by the product of " pressure times volume " 

as follows : 

v = velocity of air in feet per second; 

h = head in feet of air necessary to produce a velocity of v feet 

per second, or, 

= water pressure p in inches observed with a manometer, 

produced by the velocity of the air times the ratio of 

wt. of a cubic foot of water 



wt. of a cubic foot of air 1 



\/ 



p X 62.3 

2 £ wt. cu. ft. air for test 



(109) 



and V m = velocity in feet per minute is (taking 2 g = 64.3) 

V m = 1096.4%/— , , p . , — — — . . . . (no) 

Vwt. cu. ft. air for test 

1 Weight of air taken for calculation must be that corresponding to the total pres- 
sure in the discharge pipe, the temperature and the humidity. For tables of weight of 
air see pages 180 and 181, also Kent's "Mechanical Engineers' Pocket-Book," 8th 
edition, pages 583-588, and "Calculating and Testing Ventilating Systems," issued 
by U. S. Navy Department, Washington. 



368 



POWER PLANT TESTING 



Now the velocity in feet per minute V m multiplied by the area of the 
section at which the velocity was observed, gives cubic feet C of air 
discharged per minute, and if P is the total pressure (static + velocity) 
in pounds per square foot then we have for j the " air horse power " or 
the work done by the fan " on the air." 

CP 

j = 33^oo' t 1 ") 

and efficiency of fan E, is 

j _ CP 



E = 



33,ooo 



(112) 



Velocity measurements are usually made with a Pitot tube consisting 
essentially as shown in Figs. 224 to 225, page 179, of two tubes 
with openings at the end, arranged so that one of them " faces " in the 
direction of flow and the other extends in a radial direction. The former 
is subjected to the sum of the velocity and static pressures, while the 
latter receives only the static pressure. 

The following table of relative humidity for determinations with a 
wet- and a dry-bulb thermometer, Fig. 331, or the sling psychrometer, 
Fig. 332, as used by the U. S. Weather Bureau: 

TABLE OF RELATIVE HUMIDITY, PER CENT 



Dry 
Ther- 
mometer 
Deg. F. 



Difference between the Dry and Wet Thermometers, Deg. F. 



4 5 6 7 



9 10 11 12 13 14 15 16 17 IS 19 20 21 22 23 21 



Relative Humidity, Saturation being 100. (Barometer = 30 ins.) 



A sling psychrometer is much more accurate than the stationary wet- 
and dry-bulb type. It should be revolved at about 150 revolutions per 
minute. 

By using the above table the weight of a cubic foot of air for any 
degree of saturation and temperature can be easily calculated from the 
tables of the weight of dry air and ioo per cent saturated air as given on 
page 181. 

Anemometers are also frequently used for velocity measurements of 
air, but they are not generally so reliable as good Pitot tubes. Since, 



TESTING OF VENTILATING FAN$ OR BLOWERS 369 



however, the observations can be taken directly in feet per minute these 
instruments are used for nearly all work where no great accuracy is 
expected. 

An example showing the method of calculation for j ; the work done 
by the fan " on the air," may assist in making the method of calculation 
clearer. 

A series of Pitot-tube measurements taken at ten different places in 
the cross-section of an air duct shows that the " velocity " pressure was 
.795 and the total pressure 1.09 inches of water. The observations of 
barometric pressure and temperatures by wet- and dry-bulb thermom- 
eters, together with the " total " pressure given above, served to deter- 





Fig.] 331. —Wet- and 
Dry-Bulb Thermom- 
eters. 



Fig. 332. — Sling Psychrometer. 
(Wet- and Dry-Bulb Thermom- 
eters arranged for Rotation.) 



mine the density or the weight of a cubic foot of air at the conditions of 
the test. Barometric pressure was 39.40 inches of mercury and tem- 
peratures of wet- and dry-bulb thermometers were respectively 54 and 71 
degrees Fahrenheit. According to the tables of the properties of air (see 
footnote, page 181) this was .07449 pound per cubic foot. Velocity of 
the air V m in feet per minute is, therefore, 



V m - 1096.4 



= 3625 feet per minute. 



V .07449 

The diameter of the pipe was 10 inches, of which the area is 0.545 
square foot. Cubic feet air discharged per minute (C) are 3625 X 0.545 
or 1978. The total pressure P is the " total " pressure 1 in pounds per 

1 In this expression 13.6 is the specific gravity of mercury, .491 is a factor for chang- 
ing inches of mercury at room temperature to pounds per square inch, and 144 is used 
to change pounds per square inch to pounds per square foot. 



370 POWER PLANT TESTING 

square foot or ' ) .491 X 144 or 5.66. Work done by the fan " on 

the air " is, then, 

1978 X 5.66 
J = 33,000 = °' 34 h ° rSe p0Wer ' 

Efficiency tests should be made with the fan operating under the 
discharge pressure for which it was designed or for which] the guarantee 
was made, as the case may be. The efficiency of the fan may be consider- 
ably higher with a lower discharge pressure than when connected up in 
a ventilating system where the discharge pressure is comparatively high. 

Testing Ventilating Systems. When tests are to be made of ventilat- 
ing systems precautions should be taken in the examination of all ducts 
and piping to see that they are clear of all lumber, rubbish, etc., and that 
the dampers are properly set. The tests consist usually in measuring in 
each system the " static " and the " total " pressures with a Pitot tube 
with all louvers open. These tests should be made with the fan running 
at high, low and three or four intermediate speeds. All the results should 
be checked by plotting a curve with revolutions per minute for abscissas 
and cubic feet of air delivered per minute for ordinates. This curve 
should be approximately a straight line passing through the origin if all 
the louvers have remained open throughout the tests. On the same 
abscissas curves of pressure for ordinates will also be of advantage in 
showing the consistency of observations. The location selected for the 
testing slot to be used for inserting the Pitot tube in the mains should be 
as near as possible to the fan; preferably no branches, however small, 
should run off between the fan and the testing slots in the mains. Fur- 
thermore the testing slots should not be near turns and bends and par- 
ticularly no turns or elbows should be immediately ahead of a slot, that 
is, in the direction toward the fan. These testing slots should be covered 
when not in use. 

In the U. S. Navy Department the standard conditions adopted for 
testing ventilating fans and air-supply mains are a pressure of 5 pounds 
per square foot in the moving air at the discharge outlet from the fan and 
a velocity of 2000 feet per minute. Air at the standard conditions is 
to be at 70 degrees Fahrenheit and a relative humidity of 70 per cent. 
Under these standard conditions a cubic foot of air weighs .07465 pound. 
The pressure of 5 pounds is equivalent to a pressure head of 67 feet of 
standard density air. A velocity of 2000 feet per minute corresponds 
to a velocity head of 17.27 feet. Total head against which the air is 
delivered to the supply mains for the standard conditions is then 84.27 
feet, making a very satisfactory combination of velocity and pressure 
head, approaching as it does the maximum possible delivery for this 
pressure head. 



TESTING OF VENTILATING FANS OR BLOWERS 371 

Corrections for Losses of Total Head in Ducts. There is always some 
loss of total head along a duct or pipe due to friction. As a result there 
is a smaller delivery than that given for standard conditions. Using 
the following symbols: 

h/ = loss of head in feet due to friction; 

f = coefficient of friction = .00008 in piping of good construction; 

1 = length of duct in feet ; 

d = diameter of duct in feet; 

V m = velocity of flow through duct in feet per minute. 

h ' = n,25o"foood (II3) 

If V m = 2000 then h f = .3556 -r. 

Loss of head in a square duct is usually assumed to be the same as for 
a round one; but for a duct of rectangular section of which the short 
side is b and the long side is nb, the formula above becomes, using 1 and 
V m as before, 

1 4- n 1 V 2 

h/ = i-±-?x£x— -^ (114) 

n b 22,500,000 

With the help of these formulas when the size of the main ducts and 
the discharge in cubic feet per minute at each outlet are known, the head 
at each outlet as compared with the standard total head of 84.27 feet can 
be calculated. As a " rough and ready " rule it is often stated that for 
a loss of one foot of head there is a loss of six-tenths per cent delivery 
(cubic feet per minute). 

Testing Air Compressors. The various types of machines for com- 
pressing air are usually operated either by a steam engine or by an electric 
motor. Power delivered to the compressors by the engine or motor is 
therefore measured by one of the methods already outlined for ventilating 
fans. Air compressors, particularly of the reciprocating type, are 
designed, as a rule, for operation at considerably higher pressures than 
would be suitable for ventilating fans, and the volume delivered must 
usually be measured in a comparatively small pipe. Air at high pressure 
is generally measured by calculating the flow through an orifice in a 
receiver or one of the other methods described on pages 185 to 188. 

Foot-pounds of work " done on the air " per second; and this product 
divided by the net power required to drive the compressor is the " net " 
mechanical efficiency. (See also bottom page 373.) 

In an air compressor in which the air cylinder is direct-connected to 
the steam cylinder the net power required to drive the compressor is 
determined by finding the indicated horse power of the air cylinder and 
adding the friction in the air cylinder, which in many cases can be as- 



372 



POWER PLANT TESTING 



sumed to be half the difference between the indicated horse power as 
measured in the steam and air cylinders. For use on air compressors 
operating at high pressures special indicators are made. One of the best 
is made by the Crosby Steam Gage and Valve Co., Boston, Mass., and 
is illustrated in Fig. 333. It is similar in design to the gas engine indicator 
illustrated in Fig. 315, page 342, except that the piston in the lower 




Fig. 333. — Crosby High-pressure Indicator (Ordnance Type). 

cylinder of the indicator is very small, only one-fortieth of a square inch 
in area. This indicator can therefore be readily used for pressures as 
high as 10,000 pounds per square inch. 



RULES FOR CONDUCTING TESTS OF STEAM-DRIVEN COM- 
PRESSORS, BLOWERS AND FANS 1 

A.S.M.E. CODE OF 1912 

If the air end of a compressor is of the reciprocating type, indicator dia- 
grams should be regularly taken from this end as well as from the steam 
end. 

The rules pertaining to dry steam, heat consumption, and indicated 
horse power of the steam end, are identically the same as those given 

1 In the case of air machinery driven by some other prime mover than a steam 
engine or turbine, the code may be modified to meet the particular requirements. 



TESTING OF VENTILATING FANS OR BLOWERS 373 

on pages 296 and 297 of the Steam Engine Code, and reference may be 
made to that code for the necessary directions in these particulars. 

TESTING OF VENTILATING FANS OR BLOWERS AND AIR COMPRESSORS 

(a) Air Horse Power. The gross work done at the air end of a reciprocating machine 
expressed in horse power, is found by multiplying together the net area of the 
air piston in sq. in., the mean effective air pressure in lb. per sq. in. as determined 
from indicator diagrams, the length of the stroke in ft., and the number of 
single strokes per minute; and dividing their product by 33,000. 

The net work at the air end of either reciprocating or rotary machines, ex- 
pressed in ft.-lb. per minute, is found by multiplying the corrected volume of 
the compressed air in cu. ft. discharged into the main delivery pipe per minute, 
by the impact or total pressure in lb. per sq. ft. and by the hyperbolic logarithm 
of the ratio of the total pressure to the atmospheric pressure (all pressures be- 
ing absolute pressures). The net air horse power is found by dividing the 
product by 33,000. The corrected volume of the compressed air may be found 
by multiplying the sectional area of the delivery main in sq. ft. by the mean 
velocity in ft. per minute as determined by pitot tube or other measurement, 
and reducing the result to atmospheric temperature by multiplying by the 
proportion. 

460 + t 
460 + T 

in which t is the temperature of the air supplied to the machine and T the tem- 
perature of the air in the delivery main. 

(b) Capacity. The capacity is the number of cu. ft. of air discharged through the 
delivery main per minute, as determined by gasometer, tank or other mode of 
measurement, reduced to the equivalent free air at the atmospheric tempera- 
ture and pressure. The correction for pressure is made by multiplying by the 

P 2 
proportion — in which Pi is the atmospheric pressure and P 2 the total pressure 

Pi 
in the main (absolute pressures), and the correction for temperature as above. 

The capacity may also be expressed in the number of cu. ft. of compressed 
air discharged per minute at a given pressure above the atmosphere reduced to 
the atmospheric temperature. 

(c) Miscellaneous. For methods of calculating results pertaining especially to the 
performance of the steam-end of a reciprocating air-pumping machine, reference 
may be made to the Steam Engine Code. 

The "efficiency of compression" in a reciprocating machine is determined by 
first ascertaining the net work at the air end given above under the heading, 
(a) "Air Horse Power," and then dividing the net work thus found by the gross 
work given under the same heading. 

The " mechanical efficiency " of a reciprocating machine is determined by 
dividing the gross air horse power at the air end by the indicated horse power at 
the steam end, or by the horse power delivered by the belt or motor in the case 
of other means of driving. 

DATA AND RESULTS OF TEST OF AIR MACHINERY. CODE OF 1912 

(1) Test of located at 

to determine conducted by 

(2) Type of machinery 



374 POWER PLANT TESTING 

(3) Rated capacity in cu. ft. of free air per minute 

(4) Rated capacity in cu. ft. of air discharged per minute at 100 lbs. per sq. in. 

above atmosphere, reduced to the atmospheric temperature cu. ft. 

(5) Type of boilers 

(6) Type of auxiliaries : 

(7) Dimensions of engine or turbine at steam end 

(8) Dimensions of cylinders or blowers at air end 

(9) Dimensions of boilers 

(10) Dimensions of auxiliaries 

(11) Dimensions of condenser 

(12) Date 

(13) Duration hrs. 

Average Pressures and Temperatures 

(14) Steam pressure at boiler by gage • lbs. per sq. in. 

(15) Steam pipe pressure near throttle, by gage lbs. per sq. in. 

(16) Barometric pressure of atmosphere. . . .ins. of mercury = lbs. per sq. in. 

(17) Pressure in receiver by gage lbs. per sq. in. 

(18) Vacuum in condenser in ins. of mercury 

(19) Pressure in delivery main by gage (impact pressure) . . . •. . .lbs. per sq. in. 

(20) Total head, expressed in ft ft. 

(21) Temperature of main supply of feedwater to boilers deg. F. 

(22) Temperature of additional supplies of feedwater deg. F. 

(23) Temperature of air in engine room or air supplied to machine deg. F. 

(24) Temperature by wet-bulb thermometer deg. F. 

(25) Temperature of air in delivery main deg. F. 

Total Quantities 

(26) Water fed to boilers from main source of supply lbs. 

(27) Water fed from additional supplies lbs. 

(28) Total water fed to boilers from all sources lbs. 

(29) Moisture in steam or superheating near throttle per cent or deg. F. 

(30) Factor of correction for quality of steam, dry steam being unity 

(31) Total dry steam consumed for all purposes lbs. 

(32) Total cu. ft. of compressed air delivered as measured cu. ft. 

(33) Total cu. ft. of compressed air delivered reduced to atmospheric temperature 

and pressure cu. ft. 

(34) Total weight of air delivered lbs. 

Hourly Quantities 

(35) Water fed from main source of supply lbs. 

(36) Water fed from additional supplies ; . . . lbs. 

(37) Total water fed to boilers per hour lbs. 

(38) Total dry steam consumed per hour lbs. 

(39) Loss of steam and water per hour due to drips from main steam pipes and 

to leakage of plant lbs. 

(40) Net dry steam consumed per hour lbs. 

(41) Dry steam consumed per hour: 

(a) By main engine or turbine lbs. 

(6) By auxiliaries ; lbs. 



TESTING OF VENTILATING FANS OR BLOWERS 375 

(42) Cu. ft. of compressed air delivered per hour as measured cu. ft. 

(43) Cu. ft. of compressed air delivered per hour reduced to atmospheric tem- 

perature cu. ft. 

(44) Cu. ft. of compressed air delivered per hour reduced to atmospheric temper- 

ature and pressure cu. f t. 

(45) Weight of air delivered per hour lbs. 

Heat Data 

(46) Heat units per lb. of dry steam based on temperature Line 21 B.t.u. 

(47) Heat units per lb. of dry steam based on temperature Line 22 B.t.u. 

(48) Heat units consumed per hour based on main supply of feed B.t.u. 

(49) Heat units consumed per hour based on additional supplies of feed B.t.u. 

(50) Total heat units consumed per hour for all purposes B.t.u. 

(51) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. 

(52) Net heat units consumed per hour B.t.u. 

(53) Heat units consumed per hour : 

(a) By engine or turbine alone B.t.u. 

(6) By auxiliaries B.t.u. 

Indicator Diagrams 

(54) Mean effective pressure in steam cylinders lbs. per sq. in. 

(55) Mean effective pressure in air cylinders lbs. per sq, in. 

Speed and Stroke 

(56) Revolutions per minute 

(57) Number of single strokes per minute 

Power 

(58) Indicated horse power developed at steam end of reciprocating machine i.h.p. 

(59) Gross air horse power as indicated in air cylinders of reciprocating ma- 

chine air h.p. 

(60) Net air horse power as computed from Line 43 . air h.p. 

(61) Friction of reciprocating machine (Line 58 — Line 59) fr. h.p. 

(62) Percentage of i.h.p. lost in friction of machine per cent 

Economy Results, Steam End op Engine-driven Machines 

(63) Heat units consumed per i.h.p. per hour: 

(a) By engine or turbine and auxiliaries B.t.u. 

(b) By engine or turbine alone B.t.u. 

(c) By auxiliaries B.t.u. 

(64) Dry steam consumed per i.h.p. per hour 1 : 

(a) By engine or turbine and auxiliaries lbs. 

(6) By engine or turbine alone lbs. 

(c) By auxiliaries lbs. 

Economy Results, Air Delivered 

(65) Heat units consumed per hour per net air h.p. of Line 60: 

(a) By engine or turbine and auxiliaries B.t.u. 

(6) By engine or turbine alone B.t.u. 

(c) By auxiliaries B.t.u. 

1 The i.h.p. on which these economy results are based is that of the main engine 
given in Line 58. 



376 POWER PLANT TESTING 

(66) Dry steam consumed per hour per net h.p. of Line 60: 

(a) By engine or turbine and auxiliaries lbs. 

(b) By engine or turbine alone lbs. 

(c) By auxiliaries lbs. 

Efficiency Results 

(67) Thermal efficiency ratio for engine alone: 

(a) Per i.h.p., steam end (2545 -~- Line 636) per cent 

(6) Per net air h.p., air delivery (2545 -e- Line 656) per cent 

Work Done Per Heat Unit 

(68) Ft.-lbs. of net work per B.t.u. consumed by engine or turbine and auxiliaries 

(1,980,000 -r- Line 65a) ft.-lbs. 

Capacity 

(69) Cu. ft. of compressed air delivered per minute as measured cu. ft. 

(70) Cu. ft. of compressed air delivered per minute, reduced to atmospheric 

temperature cu. ft. 

(71) Cu. ft. of compressed air delivered per minute at 100 lbs. pressure, reduced to 

atmospheric temperature cu. ft. 

(72) Cu. ft. of compressed air delivered per minute reduced to atmospheric tem- 

perature and pressure (free air) * cu. ft. 

Miscellaneous Results 
Steam-driven Reciprocating Machine 

(73) Efficiency of compression (Line 60 4- Line 59 X 100) per cent 

(74) Mechanical efficiency of machine (Line 59 -r Line 58 X 100) per cent 

(75) Volumetric efficiency (Line 72 -f- 1st Compr. Displ. X 100) per cent 

Note. In the case of air compressors having more than one stage and in those hav- 
ing intercoolers, additional data should be given covering pressures and temperatures 
in the different stages, the quantity of water used for cooling and temperatures of the 
air and water entering and leaving the cooler. 



CHAPTER XVIII 
TESTING OF REFRIGERATION PLANTS 

Refrigerating machines present a most interesting example of the 
conversion of heat energy. In the simplest forms these machines consist 
of a compressor driven by a steam engine, or other motive power, serving 
to compress a gas or vapor as the case may be. This gas or vapor is then 
passed under pressure through a surface condenser, where the cooling 
water absorbs the heat generated in the work of compression and then 
passes into an expanding vessel into which it discharges at a very low 
temperature. Now in order to vaporize any liquid, it is necessary to 
maintain a continual application of heat in order to bring about this 
physical change. To convert a unit weight of liquid to a unit weight 
of vapor at the same pressure the heat required is always a constant 
quantity for the same liquid. Thus, as a familiar example, to convert a 
pound of water at " atmospheric " pressure and 212 degrees Fahrenheit 
into steam at the same pressure and temperature requires the application 
of 970 B.t.u.; and conversely, to condense a pound of steam at this same 
pressure and temperature, it is necessary to abstract 970 B.t.u. by contact 
with a cold body. Steam as the working medium in a refrigerating 
machine would, of course, be impracticable, because the lowest tempera- 
ture resulting from actual condensation in a workable plant would be very 
much above the freezing point of water; but there are a number of 
liquids which have a very much lower boiling point than water. Of these 
ammonia (NH 3 ), carbon dioxide (C0 2 ), and sulphurous dioxide (S0 2 ) 
are successfully used for purposes of refrigeration. The use of all these 
depends on the absorption of their latent heat in their conversion from 
a vapor or gas to the liquid condition. In practice the refrigerating 
medium most commonly used is anhydrous ammonia, although carbon 
dioxide is also frequently employed. The latter is preferred usually 
where ammonia gas might be dangerous or otherwise objectionable. 

In the simplest form of refrigerating plant the necessary machinery 
consists of (1) a compressor to raise the gas to the necessary pressure; 
(2) a surface condenser to absorb by means of cooling water the heat 
generated by the mechanical work of compression; and (3) an expanding 
or evaporating vessel where the liquid is reevaporated into a gas and, of 
course, absorbs heat in the operation. A very simple refrigerating 
machine is shown in Fig. 334. It consists of the compressor C discharg- 

377 



378 



POWER PLANT TESTING 



ing gas under pressure 1 through the pipe P into the condensing coil D, 
consisting in this simple apparatus of a coil of pipe in a tank through 
which the cooling water circulates. An expanding valve V serves for 
reducing the pressure and evaporating the liquid coming from D. The 
expanding vessel or evaporator E consists of a coil of pipe immersed in a 
tank containing the liquid to be cooled. Drops of liquid accumulate 
in the bottom coils of the condenser D, to be discharged through the 
expanding valve V into the evaporator E. Since the compressor receives 
its supply of gas from the evaporator, the pressure in the latter must be 
less than in the condenser. On this account, then, the liquid after 
expanding will begin to boil and will absorb heat from the surrounding 
liquid in its transformation into a gas. In such a process the tempera- 
ture of the cooling liquid may become very low. The refrigerating liquid 




IBM 



Fig. 334. — Typical Refrigerating Apparatus. 



in the evaporator will be entirely gasified or vaporized and returns finally 
to the compressor C in this state through the suction pipe S, thus com- 
pleting the cycle of operations. 

After this brief explanation of the principles of the operation of a 
refrigerating machine we can take up a brief discussion of the thermal 
processes as regards the interchangeability of heat and work. Using the 
symbol r for the latent heat of vaporization of the refrigerating medium 
in B.t.u. per pound, h for the heat imparted by compression in the same 
units, 2 w for the weight in pounds of the gas or vapor entering the com- 

1 In order to liquefy any gas or vapor, obviously it is necessary to bring the mole- 
cules closer together, and this can be accomplished either by increasing the pressure or 
decreasing the temperature or by both. 

2 The ratio - is often called the coefficient of efficiency of the refrigerating medium. 

h 



TESTING OF REFRIGERATION PLANTS 379 

pressor in a given time, then, neglecting external losses, wr will represent 
the heat abstracted in the evaporator and h + wr is the heat given to the 
cooling liquid in the condenser. 

In the practical operation of a refrigerating plant the evaporator is 
maintained at a very low temperature, and some heat must necessarily 
be given to it by the refrigerating medium itself, since it enters the 
evaporator, in comparison, in a moderately warm condition. Now if 
the difference in temperature between the condenser and the evaporator 
is t degrees Fahrenheit, a pound of refrigerating medium will give to the 
evaporator st B.t.u., if s is the specific heat of the refrigerating medium; 
and further if w' is the weight of this medium in pounds passing into the 
evaporator in a given time then the heat abstracted from the evaporator 
by the cooling liquid is wr — y — w'st, where y is the heat in B.t.u. lost 
by radiation. The term w'st is comparatively small in practical machines. 
If there is no leakage then, of course, w' will be the same as w. 

Anhydrous ammonia is most commonly used as the refrigerating 
medium. It is preferable to many other fluids because of its compara- 
tively high latent heat 1 and low pressure of vaporization. 

Carbon dioxide (C0 2 ), commercially known as carbonic acid, is a color- 
less gas without odor when pure, and is furthermore quite innocuous 
and has practically no injurious effect on animal tissues. It is injurious 
only when the proportion of it in air becomes so large that there remains 
an insufficient amount of oxygen. On this account, therefore, it is much 
safer and suitable as a refrigerating medium than ammonia. This gas can 
be readily liquefied either by lowering its temperature or by increasing 
the pressure. At ordinarily low temperatures it can only remain in the 
liquid state when under considerable pressure. When the pressure is 
removed, the heat absorbed from surrounding bodies assists in the rapid 
evaporation of the liquid and these bodies become correspondingly colder 
by this loss of heat. 

Carbon dioxide is used only to a limited extent, but it is found par- 
ticularly desirable on shipboard because of the compactness of the 
compressor that it requires and its inoffensive character when a leak 
occurs. 

A typical commercial refrigerating plant for making ice and operating 
with a horizontal ammonia compressor is shown in Fig. 335. The 
same descriptive letters used in Fig. 334 serve again for marking the im- 
portant parts. 

The efficiency of a refrigerating machine depends upon the difference 

1 The latent heat of vaporization of ammonia is 555 B.t.u. at a temperature of zero 
degrees Fahrenheit, while that of carbon dioxide is only 123. The corresponding 
absolute pressures at the same temperature are 30 pounds per square inch for ammonia 
and 310 for carbon dioxide. 



380 



POWER PLANT TESTING 



between the extremes of temperature, but unlike heat engines, it has the 
greatest efficiency when the range of temperatures is small and when the 
final temperature is high. 

When a change of volume of a saturated vapor is made under constant 
pressure in the presence of an excess of the liquid, the temperature 
remains constant. In this case the addition or absorption of heat to 
produce the change of volume causes an increase or decrease in the 
amount of the liquid mixed with the vapor. Vapors, even when satu- 
rated, if no longer in contact with their liquids, having heat added either 
by compression, by mechanical force or from an external source of 
heat, will behave practically like permanent gases and will become 
superheated. On this account refrigerating machines using liquefiable 




COMPLETE ICE MAKING PLANT 

Fig. 335. — Refrigerating Plant with Ammonia Compressor. 



gas will give results differing according to the conditions of operation, 
depending primarily upon the state of the gas; that is, whether it remains 
constantly saturated or is superheated during a part of the cycle. Some 
ammonia plants are operated with an excess of liquid present during 
compression so that superheating is prevented. This is known in prac- 
tice as the " wet " or " cold " system of compression. 



Density op Ammonia Vapor 



At temp. deg. C 
At temp. deg. F 
Density, lb. per cu. ft 





-10 


-5 





5 


10 


15 


. (approx.) . . 


14 


23 


32 


41 


50 


59 


cu. ft 


. 0.6492 


.6429 


.6364 


.6298 


.6230 


.6160 



20 



Ledoux found 



Latent Heat op Evaporation op Ammonia 

he = 555.5 - .613 T - 0.000219 T 2 (in B.t.u. and degrees F.) 
h e = 583.33 - .5499 T - 0.0001173 T 2 (in B.t.u. and degrees F.). 



TESTING OF REFRIGERATION PLANTS 



381 



For experimental values at different temperatures determined by 
Professor Denton, see Transactions American Society Mechanical En- 
voi. 12, page 356. For calculated values, see vol. 10, page 646. 



Specific Heat and Available Latent Heat of Hot Ammonia 

Latent heat at 15.67 lbs. per sq. in. gage press, and degrees F. = 550.5 B.t.u. 
Specific heat = 1.096 - 0.0012 T (degrees). 



Values at 15.67 lbs. per sq 


in. Gage Pressure (Lucre) 


Temperature of 

Liquid Supply, 

Deg. F. 


Specific Heat of 
Liquid. 


Correction for 
Cooling, 
B.T.U. 


Available Latent 

Heat for 

Saturated Vapor, 

B.T.U. per lb. 


5 


1.090 


5.45 


550.05 


10 


1.084 


10.84 


544.66 


15 


1.078 


16.17 


539.33 


20 


1.072 


21.44 


534.06 


25 


1.066 


26.65 


528.85 


30 


1.060 


31.80 


523.70 


35 


1.054 


36.89 


518.61 


40 


1.048 


41.92 


513.68 


45 


1.042 


46.89 


508.61 


50 


1.036 


51.80 


503.70 


55 


1.030 


56.65 


498.85 


60 


1.024 


61.44 


494.06 


65 


1.018 


66.17 


489.33 


70 


1.012 


70.84 


484.66 


75 


1.006 


75.45 


480 05 


80 


1.000 


80.00 


475.50 


85 


.994 


84.49 


471.01 


90 


.988 


88.92 


466.58 


95 


.982 


93.29 


462.21 


100 


.976 


97.60 


457.90 



The latent heat of saturated ammonia vapor as given by Lucke must 
be corrected in three ways : (1) For the temperature of the liquid, 
which must be cooled from its initial temperature to the temperature 
corresponding to the suction or back-pressure; (2) for wetness of the 
vapor, for which the correction is 5.555 B.t.u. for each per cent of mois- 
ture; (3) for superheat of vapor in case it leaves the expansion coil 
(evaporator) at a higher temperature than that corresponding to the pres- 
sure. This last correction is additive and is approximately the number 
of degrees of superheat times the specific heat of superheated ammonia 
gas taken as 0.508. 

Leakages of ammonia gas are very objectionable and may be dan- 
gerous. One of the most convenient and reliable means for locating 
a small leak is to burn a little sulphur at the end of a stick of wood about 
fifteen inches long. Where the sulphur fumes come into contact with 
the ammonia gas a white vapor is observed. 



382 POWER PLANT TESTING 

Units of Refrigeration and Capacity. A practical way to express the 
performance of a refrigerating plant is found by using as a basis the 
amount of fuel consumed and the " ice-melting " capacity 1 of the plant. 
If we use the following symbols: 

R = refrigeration of "ice-melting" capacity per pound of fuel, 

in pounds; 
w& = pounds of brine circulated per hour, pounds; 
s 6 = specific heat of brine; 

ti = temperature of brine entering expansion coils, deg. F.; 
t 2 = temperature of brine leaving expansion coils, deg. F. ; 
w f = fuel used per hour, pounds; 

R= w„s t (t 2 -t,) 

144 W/ v °' 

and the capacity C of a machine in tons, of 2000 pounds, of refrigeration 
or ice-melting per 24 hours is 

c= 2 4 W 6 S 6 (t 2 -t 1 ) 

144 X 2000 

Ice-making Capacity is usually defined as half the refrigerating capa- 
city as given by (116). 

The above are the " practical " units used in ordinary commercial 
tests. When, however, facilities are provided for determining the weight 
of refrigerating medium (ammonia, etc.) a more accurate method of 
calculation is as follows, using: 

c = refrigerating effect per lb. (ammonia, etc.) in B.t.u.; 

s = specific heat of liquid (ammonia, etc.); 

s g = specific heat of gas at constant pressure ( = 0.508 for ammonia) ; 

t s = temperature of saturated gas in evaporating coils, deg. F. (from 
tables) ; 

t e = temperature of liquid at expansion valve, deg. F.; 

t a = temperature of gas (actual) leaving evaporating coils, deg. F.; 

r, = latent heat of vaporization at temperature t s ; 

then c =T S -s (t e - t s ) +s ff (t a - t s ) (117) 

and by this method, capacity of refrigeration, C is 

C' = -^^, (118) 

288,000' 

1 Ice-melting capacity is a term applied to represent the cold produced in an in- 
sulated bath of brine, measured by the latent heat of fusion of ice, which is 144 B.t.u. 
per pound. More accurately it is the heat required to melt a pound of ice at 32 de- 
grees Fahrenheit to water at the same temperature. The capacity of a machine in 
pounds or tons of "ice-melting" or of "refrigeration" does not mean that the ma- 
chine would make that amount of ice; but that the cold produced is equivalent to 
the melting of the weight of ice to water. 



TESTING OF REFRIGERATION PLANTS 383 

when W is weight of refrigerating medium (ammonia, etc.) circulated per 
24 hours in pounds. 

As calculated by equations (117) and (118) refrigeration units are not 
comparable for different conditions of operation, and a standard of 
pressure has come to be quite generally accepted, these being 185 lbs. 
per sq. in. gage 1 pressure at the discharge of the compressor and 15.67 
lbs. also by gage and dry saturated gas at the suction. Equivalent 
refrigerating effect and equivalent tons of refrigeration at these standard 
conditions are readily calculated from equations (117) and (118), where 
the last term in (117), representing superheat, becomes zero. 

Volumetric Efficiency. The ratio of the actual volume of refrigerating 
medium, discharged from the compressor to that calculated from the 
piston displacement is called the volumetric efficiency. The following 
formula deduced from Voorhees 2 gives in most practical cases the volu- 
metric efficiency E„ of an ammonia compressor with a remarkable degree 
of accuracy: 

E _(t 1Z1 ito) (iig) 

1330 

where ti is the theoretical temperature of the gas after compression, t is 
the temperature of the gas delivered to the compressor. Here to can be 
calculated from the general equation for adiabatic compression where 

ti + 460 = (to + 460) f^Y' 24 ("9) 



Here pi and p are the absolute pressures of the gas corresponding re- 
spectively to the temperatures ti and to. The actual temperature of the 
gas discharged from the compressor will be usually considerably, some- 
times from 50 to 60 degrees Fahrenheit less than the theoretical. 

Lucke 3 has deduced the following formula for the indicated horse 
power of compressor (i.h.p.) required per ton of refrigerating capacity, 
expressed in the following symbols: 

p = the mean effective pressure in compressor in lbs. per square inch; 

1 = the length of the stroke in feet; 

a = the area of the piston in square inches; 

n = the number of compressions per minute; 

E„ = the volumetric efficiency, as defined above; 

w c = the weight of a cubic foot of ammonia vapor at the back pressure 
as it exists in the cylinder when compression begins; v c is the latent heat 
of vaporization available for refrigeration at suction pressure (see table 

1 Since gage pressures are used it is obvious our methods of calculation for refriger- 
ating machinery are not on a sound scientific basis. 

2 "Ice and Refrigeration" (1902). 

3 Proceedings American Society of Refrigerating Engineers (1908). 



384 POWER PLANT TESTING 

page 381); 288,000 = the B.t.u. equivalent to one ton of refrigeration 
per twenty-four hours, that is, 2000 X 144. Then, 

plan 

*•"*•- UB.nw.xffx 60X24 ( " 0) 

144 X 288,000 

•%*l ™ 

Theoretical Efficiency of Refrigerating Machines. The maximum 
theoretical efficiency E TO of a refrigerating machine is expressed by the 
ratio, 

Em= TT^T" ' * * (I22) 

where Ti is the highest and T is the lowest absolute temperature of the 
refrigerating medium. 

Heat Balance. The heat balance for the cycle of operation may be 
calculated as follows: The liquid enters the brine coils at a temperature 
of t e ; first: this temperature must be lowered to t a the temperature of 
saturation. Under ideal conditions (without losses) the heat added to 
the brine by this lowering of the temperature of the liquid is s(t e — t s ) 
per pound of liquid. Second, the liquid is vaporized and takes, the latent 
heat of the ammonia r s per pound of liquid from the brine. Third, if the 
temperature of the gas leaving the coils is superheated then this heat re- 
ceived by the gas from the brine in addition to'the above will be s ff (t a — t s ) 
B.t.u. per pound of ammonia. Then the total heat Hi (B.t.u.) received by 
the ammonia per pound in passing through the brine coils will be (under 
ideal conditions — no losses), using symbols as on page 382, 

Hi = r a - s(t e - t s ) + s g (ta - t s ). [Same as (117)-] 

This will also represent the amount of heat taken from the brine tank 
per pound of ammonia circulated. 

Heat received in passing from the brine tank to the compressor in 
B.t.u. per pound of ammonia gas circulated, where ti is the temperature 
of the gas at the compressor before entering, deg. F., 

H 2 = S ff (tl - ta). 

Heat Received in Passing through Suction Valves. The gas in passing 
through the suction valves of the compressor is superheated due to the 
friction and throttling when coming in contact with the hot metal in the 
cylinder. The temperature t 2 at the beginning of compression can be 
determined approximately as follows: 

t,-.t. + £x«.6-t I + £j? 1 

when d is the diameter of the compressor in inches. Then heat added 
in the valves H 3 = s„(t 2 — ti) per pound of ammonia circulated. 



TESTING OF REFRIGERATION PLANTS 385 

Heat due to Compression. The work done as shown by the indicator 
card will represent the heat added to the gas by the compressor. The 
work done on the gas is represented by the total work shown by the 
indicator cards to be taken from all the cylinders W k , which is in B.t.u. 
per pound of ammonia. 

Total Heat Added. Total heat added to the ammonia per pound of 
liquid flowing through the cycle will be 

H = Hi + H 2 + H 3 + W*. 

Heat by Jacket Water. The water flowing through the jackets of the 
compressor cylinder removes some heat from the ammonia gas, which is, 
H 4 = W](ts — U) where Wi is weight of jacket water circulated in same 
time as one pound of ammonia, also t 5 and t 4 are respectively temperatures 
of water leaving and entering, deg. F. 

Heat Absorbed by Ammonia Condenser: H 5 = r c + s ff (t 3 — t c ) in B.t.u. 
per pound of liquid. Where t c = temperature of condensed liquid in 
ammonia receiver, deg. F., r c = the corresponding latent heat, and t 3 = 
temperature of gas as discharged from the compressor. 

Heat absorbed by condensing water w 2 (t 7 — t 6 ) should equal the above 
when w 2 is weight of condensing water used while one pound of ammonia 
is circulated, also t 7 and t 6 are the temperatures of water leaving and 
entering, deg. F. 

Heat Balance. Heat added = heat absorbed + radiation (R). 

H x + H 2 + H 3 + H w = H 4 + H 5 + R (123) 

Mechanical Efficiency. The mechanical efficiency of the machine 

will be the ratio between the work done in the compressor cylinder to 

that done in the steam cylinder. 

tv/t i_ -ru* i.h.p. compressor , . 

Mech. Eff. = — t^- —. ■ (124) 

i.h.p. engine 

Ammonia Absorption Refrigerating Machines. Another class of 
refrigerating apparatus, operating by what is known as the absorption 
system, has been installed in some places. It consists of a generator 
containing a concentrated solution of ammonia in water. This generator 
is heated usually by means of a coil of pipes taking live steam from a 
boiler, although frequently the exhaust steam from engines is utilized to 
advantage. In this system a weak ammonia vapor passes first into an 
" analyzer " where some of the water is separated from the ammonia 
vapor and then into a " rectifier," where the concentrated vapor is 
cooled, precipitating still more water, and then discharges into the 
condenser coils. The lower coils of the condenser are connected to the 
upper part of the " cooler " or brine tank. An absorption chamber is 
provided which is filled with a weak solution of ammonia, and this 



386 POWER PLANT TESTING 

chamber is also connected with the cooling tank. The absorption 
chamber communicates with generator by two tubes, one going to the 
bottom of the generator from the top of the chamber, and the other from 
the bottom of the chamber to the top of the generator. In the latter 
pipe line, a pump is located to force the liquid from the absorption cham- 
ber, where the pressure is about atmospheric, to the generator, where 
the pressure is from 100 to 200 pounds per square inch. In the operation 
of this apparatus the ammonia and water in the generator are first 
heated by the coil of steam pipes, and as the ammonia is freed from 
the solution the pressure rises. When this pressure attains that of 
saturated vapor at the temperature of the condenser it becomes liquefied, 
condensing also a small amount of steam. A suitable expansion valve 
regulates the flow of the liquefied gas into the refrigerating coils in 
the cooler. As it escapes into these coils it expands and is again vapor- 
ized, absorbing heat from the liquid or gas required to be cooled. Just 
as rapidly as vaporization goes on the gas is absorbed by the weak solution 
in the absorbing chamber. The heat in the generator has the effect of 
separating a strong from a weak solution, the greater concentration 
being in the upper part. The weaker portion of the solution is con- 
veyed by the pipe entering the top of the absorption chamber. The 
satisfactory operation of this apparatus depends upon careful adjust- 
ments and regulation of the flow of gas and liquid, controlling in this way 
the temperature in the cooler. 

Testing of Refrigerating Plants. The primary object of a test of a re- 
frigerating apparatus is to compare the refrigerating effect with the heat 
equivalent of the mechanical work and of the cooling of the water or 
brine. The making of ice is not satisfactory for accurate results in a test. 
The range of temperature should not be greater than necessary to secure 
accuracy in the thermometer readings. The brine should be measured 
or weighed in suitable tanks as for the condensed steam in engine 
tests. 

One of the most important precautions to be observed is to determine 
accurately the specific heat of the brine for the temperature range of 
the test. Small differences in its concentration and composition may 
produce a considerable variation in results. When a compressor and 
steam engine are coupled directly together on the same shaft a direct 
measurement of the power required for the compresser is not obtain- 
able. By measuring the horse power of the engine running without 
doing any work in the compressor — that is, operating it " empty " — 
and by comparing the differences in power between the steam engine 
and compressor for wide variations of condenser pressure, the effective 
horse power required to drive the refrigerating machine can be determined 
with some degree of accuracy. 



TESTING OF REFRIGERATION PLANTS 387 

The following data sheet is used in parts by Denton 1 : 

1. Average high ammonia pressure above atmosphere 

2. Average back ammonia pressure above atmosphere 

3. Average temperature brine inlet 

4. Average temperature brine outlet 

5. Average range of temperature 

6. Lbs. of brine circulated per minute 

6a. Specific heat of brine 

7. Average temperature condensing water at inlet 

8. Average temperature condensing water at outlet 

9. Average range of temperature 

10. Lbs. water circulated per minute through condenser 

11. Lbs. water per minute through jacket 

12. Range of temperature in jackets 

13. Lbs. ammonia circulated per minute 

14. Probable temperature of liquid ammonia entrance to brine-tank 

15. Temperature ammonia corresponding to average back pressure 

16. Average temperature of gas leaving brine tank 

17. Temperature of gas entering compressor 

18. Average temperature of gas leaving compressor 

19. Average temperature of gas entering condenser 

20. Temperature due to condensing pressure 

21. Heat given ammonia: 

By brine per B.t.u. per minute 

By compressor, B.t.u. per minute 

By atmosphere, B.t.u. per minute 

22. Total heat received by ammonia, B.t.u. per minute 

23. Heat taken from ammonia: 

By condenser, B.t.u. per minute 

By jackets, B.t.u. per minute 

By atmosphere, B.t.u. per minute 

24. Total heat rejected by ammonia, B.t.u. per minute 

25. Difference of heat received and rejected, B.t.u. per minute 

26. Per cent of work of compression removed by jackets 

27. Average revolutions per minute 

28. Mean effective pressure steam cylinder, lbs. per square in 

29. Mean effective pressure ammonia cylinder, lbs. per square in 

30. Average H.P. steam cylinder 

31. Average H.P. ammonia cylinder 

32. Friction in per cent of steam H.P 

33. Total cooling water, gallons per minute, per ton ice-melting capacity per 24 hours . 

34. Tons ice-melting capacity per 24 hours 

35. Lbs. ice-refrigeration effect per lb. coal at 3 lbs. per H.P. hour 

36. Cost coal per ton of ice-refrigerating effect at $4 per ton 

37. Cost water per ton of ice-refrigerating effect at $1 per 1000 cu. ft. per 24 hours. . . 

38. Total cost of 1 ton ice-refrigeration effect 

39. Refrigeration effect per I. H.P. in compress, cyl., B.t.u. per minute 

40. Refrigeration effect per I. H.P. in steam, cyl., B.t.u. per minute 

41. Refrigeration effect per pound of steam, B.t.u. per minute 

1 Transactions American Society of Mechanical Engineers, Vol. 12, page 356. 



388 POWER PLANT TESTING 

Another form for data and results, including a heat balance is as 
follows : 

RESULTS OF REFRIGERATING PLANT TESTS 
General 
1. Date of test located at 



2. Object of test 

3. Duration of test 

4. Type of machine 

5. Dimensions: 

6. Diam. of ammonia cyl diam. steam cyl 

7. Stroke of compressor stroke of steam engine . . . 

8. Diam. of piston rod comp. cyl diam. piston rod steam cyl 

9. Average Temperatures of Ammonia: Leaving machine. . . . entering machine 

10. Leaving condenser .... entering expansion coils 

11. Leaving expansion coils 

12. Average temperatures of water: 

13. Entering ammonia condenser .... leaving ammonia cond 

14. Entering compressor jackets .... leaving comp. jackets : 

15. General temperatures: All temperature in degrees 

16. Room .... outside air .... brine 

17. Pressures: (Lbs. per sq. inch absolute.) 

18. Steam .... discharge, ammonia .... suction ammonia 

19. Atmospheric 

20. Weights: (pounds.) 

21. Ammonia used .... jacket water .... ammonia condenser 

22. Ammonia per hour .... jacket water per hour 

23. Ammonia condensed per hr ammonia per 24 hrs 

24. Jacket water per 24 hrs ammonia cond. per 24 hrs 

25. Scale of spring, ammonia cylinder lbs. per sq. in. 

26. Scale of spring, engine cylinder r.p.m. 

27. Average i.h.p. per hour (steam cylinder) 

28. Average i.h.p. per hour (ammonia comp.) 

29. Condition of gas leaving machine deg. F. sup. 

30. Condition of gas at beginning of compression deg. F. sup. 

31. Condition of gas entering machine deg. F. sup. 

32. Refrigerating effect, actual, per lb. ammonia B.t.u. 

33. Tons of refrigeration, actual 

34. Ice-making capacity, actual (line 33 -f- 2) tons 

35. Mechanical efficiency per cent 

36. Equivalent refrigerating effect based on standard conditions (seepage383) B.t.u. per lb. 

37. Equivalent tons of refrigeration based on standard conditions (see page 382) 

38. Ice-making capacity based on standard conditions tons 

39. Per cent rating obtained 

40. Volumetric efficiency (see page 383) per cent 

41. Heat balance (see pages 384) 



CHAPTER XIX 



TESTING OF HOT-AIR ENGINES 



Hot-air Engines of the conventional type are reciprocating " piston " 
engines which are operated by the alternate expansion and contraction 
of a charge of air. This alternate expansion and contraction is pro- 
duced by heating and cooling. 



Engines of this kind now in use 
are found most often in country 
places, where they are used for 
pumping water. Usually coal is 
burned for fuel; but sometimes 
gas is used, particularly in the 
natural-gas districts. 

Rider Hot-air Engine. The 
most successful engine of this 
kind is made by the Rider-Erics- 
son Engine Company of New 
York. This engine, illustrated 
in Fig. 336, consists of a com- 
pression cylinder C and a power 
cylinder P, each provided with a 
separate piston. These two cyl- 
inders are connected together by 
a rectangular passage R contain- 
ing a large number of thin metal- 
lic plates and forming what is 
called in engines of this type the 
regenerator. This regenerator 
has for its function the alternate 
abstracting and returning to the 
air of a quantity of heat. Air 
leaking out is replaced by a 
fresh supply admitted through 
the check valve V, which opens inward, 
provided with a water-jacket. 

The cycle of operations in this engine consists of a compression stroke 
when the piston in the compression cylinder C compresses the cold 




C- Compression Cylinder 
p -Power Cylinder 
E- Cooler 
H -Heater 
R- Regenerator 
II -Cranks set at about 100° 
JJ-Connecting Rods 



L-Check Valve 
M-Pump Primer 
T— Water Jacket, to 

protect packing 

fromjieat 
U-Pump 



Fig. 336. — Hot-air Engine. 

The compression cylinder C is 



390 POWER PLANT TESTING 

air from which the heat has been abstracted by its passage through the 
regenerator R, and then by the simultaneous advancing upward move- 
ment of the piston in the power cylinder P the air passes again through 
the regenerator and also through the heater H without appreciable 
change of volume. As a result the addition of heat increases the pres- 
sure of the air and when it enters the power cylinder P it pushes the piston 
upward to the end of its stroke. This upward movement of the power 
piston in the last half of its stroke carries with it the piston in the com- 
pression cylinder C, which is on the same shaft but set at an angle of 
90 degrees, so that the two pistons do not reach the ends of their strokes 
together. Now as the charge of air cools the pressure falls, so that 
the piston in the power cylinder falls and in the last half of this stroke 
carries downward with it the piston in the compression cylinder and 
again starts compressing the charge of air. As the heated air passed 
through the regenerator plates on its way to the compression cylinder 
the greater portion of the heat it contained was left in them to be ab- 
stracted on the return movement to be used again for increasing the 
temperature of the charge. 

In Fig. 336 a water pump U is shown at the left-hand side of the 
engine. Besides being used for supplying a water system it pumps 
the cooling water needed for the water-jacket T and the cooler E. 

Tests of Hot-air Engines do not differ in the important details from 
tests of steam and gas engines. The indicated horse power is obtained 
by attaching engine indicators to both the power and the working 
cylinders and the net indicated horse power is the difference between 
that for the power and that for the compression cylinders. A Prony 
brake or similar device attached to the main shaft for absorbing the power 
can be used to determine the useful or brake horse power and the ratio of 
the brake to the indicated horse power is the mechanical efficiency. 

For testing such engine to determine the efficiencies and economy it 
is preferable to use gas or oil for fuel instead of coal, because of the 
obvious advantages in the determination of fuel consumption. 

Thermodynamic efficiency is the ratio of the range of temperature 
to the initial absolute temperature of the air in the power cylinder. 
Temperatures not determinable by direct measurement may be calcu- 
lated from the pressures and the specific volumes by the general formula 
for perfect gases, 

T = pv/R, (122) 

where R for air is 53.21. 



CHAPTER XX 



TESTS OF HOISTS, BELTS AND FRICTION WHEELS 



Efficiency of Hoists. An efficiency test of a hoist is made by deter- 
mining the ratio between the work done in lifting the load to that applied 
to the hand chain. Stated briefly, this determination is made by raising 
slowly a known weight, observing at the same time by means of a spring 
balance fastened to the hand chain, the pull or force required to keep the 
load moving after it has been started. The method is, of course, the 
same for determining the efficiency of a rope hoist, except that some 
special provision must be made for attaching the hook of the spring 
balance to the rope. Allowance must also be made, of course, for the 
number of times the power is multiplied, that is, the relative velocity 
value. 

Differential Hoists. Differential hoists (Fig. 337) are a little more 
complicated than the ordinary chain or rope hoist. In this apparatus, 
as shown in the standard books on the theory of 
mechanism, the velocity ratio is expressed according 
to the dimensions in the figure by 

2R1 * , 

r7^r 2 (I23) 

It is difficult, however, to measure accurately the 
radius of these wheels on account of the irregular 
surface made for gripping the links. Now since the 
circumferences of these wheels are proportional to the 
radii, the velocity ratio may be determined by count- 
ing the number of link-pockets in each of the wheels, 
and its value will be given by the ratio of twice the 
number of link-pockets in the larger wheel divided by 
the difference between the number of link-pockets in 
the larger and the smaller wheels. In some other 
types of hoists where this method is not applicable 
and the diameters cannot be readily measured, the 
velocity ratio can be determined by tying a piece of 
string on a link of the " load " chain or rope, as the case may be, oppo- 
site some fixed part of the hoist and mark ir the same way a point on 
the chain or rope to which the pull is appliec Now when the "load" 
chain has been moved a measured distance, /he corresponding move- 

391 




Fig. 337. — Differ- 
ential Hoist. 



392 POWER PLANT TESTING 

ment of the point of application can be measured. Several observations 
should be made to eliminate probable errors in the measurements. 
Velocity ratio is usually expressed by making the second member of the 
ratio unity, thus 13 : 1, 4 : 1, etc. 

The force required to move the hand chain by the spring balance 
multiplied by the velocity ratio is the work " put into " the hoist, while 
the weight lifted is proportional to the work done. Efficiency is then 
the work done divided by the work " put in," or in the terms above is the 
weight lifted divided by the product of the pull on the hand chain 
times the velocity ratio. 1 On account of the great friction at starting 
the reading of the spring balance should be made when constant after 
starting by hand. Determinations should also be made when the load 
is being lowered, but these results should not be averaged with those for 
raising the load because a hoist is generally used only for raising loads. 
Determination of Tension in Belts and Rope Drives. Tests are often 
required to determine the power transmitted by belts and ropes for 
specified conditions of load, speed, tension, and the coefficient of friction 
between these and the pulleys on which they run. Suitable apparatus 
for such tests consists of a device with which the belts or ropes can be 
operated with different tensions. Usually the load is not increased be- 
yond the limit producing 3 per cent slip. 2 The initial tension in the belt 
or rope should be measured when at rest. 

Testing of Belts. For determining the qualities of belts as regards 
power transmission and the coefficient of friction belt tests are desirable. 
_^X 3 Sometimes belts or pulleys of different mate- 

rials are to be compared, while again tests 
may be required to determine the effect of 
belt dressings. The apparatus to be described 
is simple in construction and inexpensive. It 
consists essentially of two pulleys on the ends 
of a universal coupling. One of these pulleys 
is driven by a variable speed motor to which 

^ ooo nn j ™ it is belted. The other is set up on the frame 
Fig. 338. — Belt and Rope . i . ,. , 

Testing Apparatus. shown m Fig. 338 suspended on a knife-edge 

bearing at O so that the end at S is free to 
move in a vertical plane and any horizontal tension in a belt placed on 
it produces a proportional r ressure on a scales at S. This pulley shown 
in the figure is the driver f :>r another pulley attached to shafting about 

1 If the spring balance is us< d in the inverted position, its weight must be added 
to the pull. Also the weight o the scale pans used for supporting the weights must 
be added. 

2 Slip in belts or ropes is rat > of the difference between the revolutions of the driver 
and the follower divided by th revolutions of the driver, each taken, of course, for the 
same time unit. 




TESTS OF HOISTS, BELTS AND FRICTION WHEELS 393 

25 feet away in fixed bearings and is attached to a Prony brake. This 
last shaft is adjustable in its bearings so that the tension in the belt can 
be varied. 

Let Ti = tension in tight side of belt, lbs.; 
T 2 = tension in slack side of belt, lbs.; 
W = pressure on scales at S, lbs; 

then (T 1 + T 2 )a=Wb or Ti + T 2 = — (124) 

a 

When power is being transmitted by the belt and absorbed by the 
Prony brake we have, since the power transmitted is proportional to the 
difference of tension, by moments wR + T 2 r = Tir, and then 

Ti-T 2 =^, (125) 

where 

w = net weight on brake, lbs.; 
R = length of brake arm, ft.; 
r = radius of driven pulley, ft. 

Combining (124) and (125) 

Wb wR 

Ti= a 2 r (126) 

WbwR 
„, a r 



(127) 



These last equations give the total tensions Ti and T 2 which are usually 
reduced to pounds per inch of width of the belt. 

The coefficient of friction (f) between the belt and the pulley is given 
in books on Mechanics as 

logsr 

• • (128) 



0.434 C 



where c is the arc of contact of the belt on the pulley in inches divided 
by the radius of the pulley in inches. 

Belts will be stretched more on the tight than on the slack side and this 
unequal stretching causes a difference in velocity, or per unit of time, a 
difference between the length of belt on the driving and driven pulleys. 
This difference is called the creek or slip of the belt. If r' is the radius 
and N' the r.p.m. of the driving pulley, while r is the radius and N 
is the r.p.m. of the driven pulley then the difference in velocity is 
2 7rr'N' — 2 71-rN. This is because the length of belting coming on a 



394 . POWER PLANT TESTING 

pulley in a unit of time is equal to its peripheral speed. Slip or creek is 
expressed usually as a percentage of the speed of the driver so that 

r'N' — rN 
Percentage slip or creek = ^ — (129) 

Efficiency of Transmission = Delivered Horse Power 4- Horse Power 
Input. 

Tests of Friction Wheels. The apparatus frequently used for deter- 
mining the coefficient of friction between friction wheels consists of a 
pair of pulleys, one of them at least usually made of some soft metal like 
aluminum or a fibrous material like straw fiber, leather fiber or paper. 
This driver runs on a follower generally of some other material. Power 
delivered to the " follower " shaft is absorbed by the Prony brake. A 
bell-crank lever to which weights can be attached is used to hold or press 
the two pulleys together. 

The coefficient of friction as determined by such an apparatus is the 
ratio of the tangential pull to the total normal pressure. If the coefficient 
of friction is represented by f , and other symbols are used as follows : 

ri = the effective brake arm in inches; 

x<l = the radius of driven pulley; 

W = net weight on the brake in pounds; 

p = normal pressure in pounds per inch of width; 

z = width of the narrower pulley in inches; 

then, 

WTi 

f-i-^ ( I3 o) 

pz pr 2 z 



CHAPTER XXI 

TESTING OF LUBRICANTS 

In the space which can be taken for this chapter on the testing of oils, 
only a few of the simpler and more important tests can be given. To 
make a complete report on the composition of a sample of oil it is gener- 
ally advisable to submit the suspected sample to a competent professional 
chemist, preferably with a large and varied experience in the analysis 
of lubricants. Characteristic tests, however, will be given here which 
should be sufficiently serviceable to engineers to determine whether an 
oil is sufficiently pure for the use intended and whether, if it is to be used 
as a lubricant, it has the properties essential for reducing friction to a 
minimum, or if used as a fuel, it is necessary to ascertain the degree to 
which it is susceptible to vaporization, and in the case of very light oils, 
the temperature to which it may be exposed without danger of becoming 
inflammable. The heating or calorific value of fuel oils is also a very 
important test, but this has been explained in Chapter VIII. It 
remains therefore only to take up for fuel oils the tests for specific gravity 
and the flash and burning points. 

Specific gravity of a liquid is determined most accurately in most cases 
where a sensitive chemist's balance is available, by the use of a specific 
gravity bottle. A conventional type is shown in Fig. 340. Bottles for 
this purpose are made with special care of thin glass and the weight of 
distilled water which they will contain is determined accurately and 
etched on the outside surface of the bottle. The bottle is provided with 
a small " ground " glass stopper having a capillary tube or hole drilled 
through it, so that when the bottle is filled to the top of the capillary tube 
it will always hold the same volume of liquid. 

In the operation of determining the specific gravity the bottle is filled 
with the liquid to be tested being careful to avoid the formation of air 
bubbles. The stopper is then inserted and some of the liquid will run 
out through the capillary tube. This excess should be wiped off so that 
the bottle will be clean and dry. It can then be weighed. After once 
determining the weight of the bottle filled with distilled water at 60 
degrees Fahrenheit the bottle can be used without again weighing it 
with water. 1 The weight of the empty bottle should be ascertained from 

1 This suggestion is made because it is not always easy for engineers to obtain clean 
distilled water. Condensed steam from a surface condenser is usually, however, 
sufficiently free from impurities, and is, of course, distilled water. 

395 



396 



POWER PLANT TESTING 



time to time to determine, more than for any other reason, whether it is 
clean. If it is found to weigh more than when new,, obviously it needs 
cleaning. The weight of the liquid in the bottle when it is full divided 
by the weight of the corresponding amount of distilled water is the 
specific gravity of the liquid being investigated. The liquid tested should 
be at 60 degrees Fahrenheit when it is weighed in the bottle, as this is 
the standard temperature for the specific gravities of all oils. 

For the determination of the specific gravity of very thick oils and 
greases, a type of bottle or tube known as Hubbard's (Fig. 341) is often 
used. It consists of a metallic tube with a ground-in stopper, having 
a slightly larger bore than the capillary tube in the glass stopper of the 
ordinary specific gravity bottle. In commercial practice the specific 





M 



Fig. 340. —Specific 
Gravity Bottle for 
Thin Oils. 



Fig. 341. — Specific 
Gravity Bottle for 
Thick Oils. 



ffl 



Fig. 342. — Hydrom- 
eter and Hydrome- 
ter Jar. 



gravity of liquids is usually determined by means of an instrument called 
a hydrometer, Fig. 342. It is most conveniently used by filling a glass 
jar, preferably similar to the one in the figure, with the liquid to be 
tested and then inserting the hydrometer. The reading on the scale 
of this instrument which is at the level of the surface of the liquid is the 
specific gravity. The hydrometer shown has a thermometer combined 
with it, so that the temperature of the liquid can be read on the scale of 
the upper stem. The " surface of the liquid " is here understood to 
mean the surface of the main body of the liquid and not the level of the 
ring around the instrument due to capillarity. Hydrometers are made 
with two standard scales. One is the ordinary specific gravity scale 
graduated to correspond to the determinations of specific gravity as 
defined for determinations with the specific gravity bottle; that is, using 
always the ratio of the weight of the liquid to the weight of an equal 
volume of water. The other is an arbitrary one known as Baume's 



TESTING OF LUBRICANTS 



397 



and is much used by trades people. For short, it is often called the 
" gravity " scale. The following condensed table will be found con- 
venient for converting one scale to the other. As a " rule of thumb " 
key to^the two scales, it will be found useful to remember that 70 in the 
Baume scale is approximately 0.70 in specific gravity. 



Baum6. 


Specific Gravity. 


Baume. 


Specific Gravity. 


10 


1.0000 


60 


0.7368 


20 


0.9333 


65 


0.7179 


30 


0.8750 


70 


0.7000 


40 


0.8235 


75 


0.6829 


50 


0.7777 


80 


0.6666 


55 


0.7567 


85 


0.6511 




Sometimes engineers will find it necessary to determine the specific 
gravity of liquids when suitable instruments are not available. Fig. 344 
shows a device which can be conveniently used in 
such cases. It consists of two U-tubes with one of 
the ends of each connected together by rubber tub- 
ing. Each U-tube is provided with the usual scale 
for observing the difference in level of the liquid in 
the tubes. One of these tubes is to be filled with 
clean distilled water (condensed steam) and the 
other with the liquid to be tested. When a slight 
pressure is produced in the tubes A and B, as 
for example by blowing with the mouth, the differ- 
ences in level of the liquids in the two tubes is to 
be observed. The difference in level will be great- 
est, of course, in the tube having the lighter liquid. 
The ratio of the difference in level in the U-tube 
containing water to the difference in the level in the U-tube containing 
the liquid being tested is the specific gravity required. In the figure 
shown if the U-tube A contains distilled water and B the liquid being 
tested, and the water is displaced a inches and the other liquid b inches, 
then the specific gravity is a -4- b. The advantage of this sort of device 
is that it can be made up in any place where merely glass and rubber 
tubing are available. 

Viscosity Test. Every experienced user of oils knows how to deter- 
mine roughly the relative fluidity or what he calls the " body " of an oil 
by rubbing it between his thumb and fingers. But such a test gives us 
no definite standard of comparison. In technical language this relative 
fluidity or " body " is called viscosity. It is generally accepted that the 
viscosity determination is a most important test of the lubricating 



Fig. 344. — Simple De- 
vice for Determining 
Specific Gravity. 



398 POWER PLANT TESTING 

qualities of an oil. In general the higher the viscosity the greater the 
lubricating value, but it should be observed, however, that care must be 
taken in interpreting the results of such tests because it does not follow, 
particularly in the case of light, high speed machinery, that a highly 
viscous lubricant like castor oil would lubricate a spindle for such ma- 
chinery better than a " thin " sperm oil. In other words as regards 
viscosity the lubricant must be selected with due consideration to the 
kind of work to be done. 1 

A lubricant is applied to the bearings of machinery to keep the metallic 
surfaces moving over each other without coming into direct contact. 
Unless the surfaces are kept apart by some suitable fluid substance the 
irregularities which exist on all surfaces, no matter how carefully they are 
made, will tend to interlock, and the friction caused by forcing or pushing 
them apart will generate heat. It is the function of a lubricant to flow 
between the closely fitting surfaces of a bearing and maintain always a 
thin fluid film to act as a cushion separating the solid particles of the 
bearing surfaces as well as to take up and carry away either by a direct 
flow or by vaporization a large part of the heat generated by friction. 

Viscosimeters are instruments designed to determine the viscosity 
of oils. There is no generally accepted standard for such tests as various 
types of instruments are used; and the results with different instru- 
ments will often vary considerably. Unless the names of the designer 
and maker of the instrument used and the amount and temperature of 
oil used are stated results are almost meaningless. 

It is generally considered necessary to make determinations of the 
viscosity of the so-called engine, dynamo, and machine oils at 70 degrees 
Fahrenheit, which is considered the normal temperature in engine and 
dynamo rooms and in workshops, and again at about 120 degrees which 
is the temperature of a bearing that is running quite warm. Very often 
it will be observed that of two samples of engine oil showing the same 

1 Further in regard to the purely physical properties of oils the viscosity determina- 
tion is a test for the combined effects of both cohesion and adhesion. A good lubricant 
must have both of these properties to possess a satisfactory "body." Cohesion, as it 
were, binds together the particles of oil. The more cohesion there is between the 
particles the greater the pressure or force they will resist before separating. High co- 
hesive value is therefore essential in lubricants intended for heavy machinery. Ad- 
hesion is the running-mate of cohesion. It is the property of particles of one body 
adhering to particles of another body of different constitution. An oil with satisfactory 
adhesive qualities will stick or adhere closely to the surface of metallic bearings, and 
thus assist the cohesive qualities by helping to resist the separation of the particles of 
the lubricant under pressure. A fluid having high cohesive properties and little ad- 
hesion would be a poor lubricant, as, for example, mercury; and conversely great ad- 
hesive qualities without those of cohesion as in the case of water, alcohol, etc., are 
equally unsatisfactory. A good lubricant must have these two qualities jointly to 
make it viscous. 



TESTING OF LUBRICANTS 



399 



viscosity as 70 degrees, one will test considerably higher at 120 degrees 
than the other. Cylinder and gas-engine oils should be tested for vis- 
cosity at 100, 200 and 300 degrees Fahrenheit; or if the cylinder oil is 
used in engines using superheated steam or the gas-engine oil is for 
internal combustion engines using extremely high compression, even 
higher limits of temperatures should be used in testing. 1 The best 
lubricant for a bearing under normal conditions may not do so well 
when heating begins. An oil which under ordinary conditions would 
be much too viscous for light, high-speed machinery so as to be very 
wasteful of power is often most serviceable in a hot bearing when the 
engine oil ordinarily used vaporizes as soon as it enters and therefore 
serves no useful purpose. Heavy cylinder oil, however, since it 
vaporizes at a much higher temperature than the engine oil will be 
heated only enough to make it thin and limpid without burning and 
will flow freely between the surfaces of the bearing, keeping the sur- 
faces apart and at the same time conveying away much of the heat 
generated. 

Types of Viscosimeters. One of the simplest instruments and 
probably the one most used in America for determining the viscosity 
of oils is shown in Fig. 345. It is known as 
Scott's and consists of a metal cup with an 
orifice at the bottom and is surrounded by an 
outer vessel also made of metal which for low- 
temperature determinations is filled with water. 
For tests at temperatures above the boiling- 
point of water the vessel is to be filled with 
some kind of oil vaporizing at a temperature 
higher than that required for the tests to be 
made. The outer vessel is not circular but has 
a side extension shown on the right-hand side 
in the figure, under which a gas burner or an 
oil lamp can be placed for heating the liquid 
surrounding the inner cup containing the oil to 
be tested. By this means the oil in the cup 
can be heated uniformly to any desired temper- 
ature. The orifice is kept closed by means of a ball valve on a rod 
which extends up through the cover. The valve is lifted to allow the 
flow of oil through the orifice by pressing down with the finger on the 
end of the lever A. The handle H is provided for lifting out the oil cup 




Fig. 



345. — Simple Type of 
Viscosimeter. 



1 When oils are to be tested at temperatures above about 200 deg. Fahrenheit usually 
the sample tested is heated by means of a bath of engine oil instead of water in the 
outer receptacle of a viscosimeter, particularly those of the "orifice" type where the 
direct application of a flame is impracticable. 



400 POWER PLANT TESTING 

so that it can be readily cleaned. A thermometer T registers the tem- 
perature of the oil. For draining the water or oil in the outer vessel a 
cock C is provided, and a glass cylindrical flask accurately graduated in 
cubic centimeters is supplied for measuring the discharge from the 
orifice. 

To operate this apparatus first fill the oil cup with about 200 cubic 
centimeters. In this apparatus it is necessary to start always with 
exactly the same amount of oil in the cup; otherwise there will be vari- 
able heads (pressures) on the orifice for different tests, introducing 
corresponding errors in the flow of the oil to be tested. Fill the outer 
vessel with water and heat the latter until the oil- is at the required tem- 
perature for the test. Maintain this temperature constant for two or 
three minutes and then place a 50-cubic-centimeter flask under the 
orifice and by removing the ball valve start the flow of oil observing 
the time as accurately as possible, preferably to the fraction of a second. 
When the level of the oil in the flask has reached the 50-cubic-centi- 
meter mark close the ball valve and again observe tin time. The 
number of seconds required for 50 cubics centimeters of a liquid to flow 
through the orifice is called the time viscosity. Usually instruments 
of this kind have the water viscosity marked on the name-plate. This 
is the number of seconds required for 50 cubic centimeters of distilled 
water at 6o degrees Fahrenheit to be discharged from the orifice. The 
water viscosity should be checked from time to time because there is 
sometimes a small accumulation of grease in the orifice which may 
remain unobserved and would reduce the actual or effective size of the 
orifice. Some basis for comparison of determinations of viscosity made 
by the various types of viscosimeters in which the discharge from an 
orifice is applied can be obtained by calculating what is called the 
specific viscosity. This is the time viscosity divided by the water 
viscosity. Thus if for a given apparatus the time viscosity is 120 seconds 
and the water viscosity is 10, then the specific viscosity is 12. 1 

Redwood's and Engler's viscosimeters are practically the same as 
the one described (Scott's). Redwood's is largely used in England and 
Engler's is the one officially adopted by the German government. None 
of the types described have orifices of exactly the same size. 

Flash-point Testers. The instrument which has been shown by 
elaborate tests to be by far the most accurate and reliable is known as 

1 Sometimes when oils of very different specific gravities are to be compared a 
correction is applied to offset the difference in flow through the orifice, causing the 
heavier oil to flow faster than a lighter one. Thus we obtain the gravimetric viscosity 
for comparison which is determined by dividing the specific viscosity by the specific 
gravity. For nearly all practical work the specific viscosity gives a sufficiently good 
basis for comparison of oils. 



TESTING OF LUBRICANTS 



401 



the Abel-Pensky tester. 1 An improved model as developed by the U. S. 
Bureau of Mines is shown in Fig. 346. It consists of a central oil cup 
A to hold the sample to be tested, C a water-bath heated by 
the Bunsen burner B, an overflow D for oil expanding by heat, E an 
overflow cup, S a stirrer driven from the 
pulley P at the top, T! a thermometer for 
determining the temperature of the oil 
and To for the temperature of the water- 
bath, G a small gas flame mechanically 
operated to expose the vapor from the 
oil cup for exactly one second, and H an 
ivory head with which to judge the stand- 
ard size of the test flame. This appa- 
ratus is considerably more complicated 
than the apparatus ordinarily used for 
flash tests. Complications come mostly 
in providing a stirring device and a me- 
chanical device for applying the test flame. 
The top of the oil cup is closed except for 
a small aperture which is opened when 
the test flame is applied. 

Duration of the exposure to the test 
flame is important. Frequent opening of 
the aperture to expose the test flame per- 
mits frequent escape of the vapors and 
raises the flash point. Exposing the flame 
at each degree Fahrenheit rise in temper- 
ature is recommended. 

The testing or exposure of the test flame 
should begin at least ten degrees Fahren- 
heit below the estimated flash point. 

The differences of temperature at different points within the oil 
in the ordinary unstirred cup may be as much as from 5 to 10 degrees 
Fahrenheit. Oil is hottest along the bottom and sides of the cup. The 
heated oil rises to the surface along the sides, then flows down the 
center. Therefore the oil and vapors should be stirred during the test. 

A coal-gas test flame gives a flash point nearly a degree Fahrenheit 
lower than an oil test flame. An electric test spark gives a variable but 
usually a lower result than a gas flame. Since it is not possible to control 
the intensity and duration of the electric spark an electric test spark, 
should not be used. 

1 For a more complete description see Technical Paper No. 49, U.S. Bureau of 
Mines, Washington^ D. C. 




Fig. 346. — U. S. Bureau of Mines 
Type of Viscosimeter. 



402 POWER PLANT TESTING 

Burning point of an oil is the temperature at which the oil ignites and 
continues to burn in the cup with the cover removed. This will be 
usually 5 to 20 degrees Fahrenheit higher than the flash point. The 
difference is greater for a mixture of light and heavy oil than for a norm- 
ally refined petroleum product. 

The sample and the oil cup must first be brought to a temperature of 
about 20 deg. F. below the approximate flash point of the oil, by standing 
the cup in an ice mixture or warming the sample as may be found neces- 
sary before the cup is adjusted in the bath. The lower edge of the 
overflow aperture D is greased on its outer side to induce ready overflow 
when the oil expands. The clean, dry cup is then placed in the bath, the 
sample is run into the cup with the aid of a glass pipette until the filling 
point just disappears under the surface as seen by light reflected from the 
surface of the oil. Care must be taken not to splash the oil on the sides 
of the cup and not to have froth formed on the oil. All bubbles on the 
surface of the oil must be pricked with a heated wire. In case too much 
oil has been accidently run into the cup, the cup must be emptied, washed 
clean with a good solvent, wiped dry, and a fresh filling made. After the 
filling is correctly done, adjust the cover and thermometer immediately, 
light the test flame, and adjust it to the size of the ivory bead on the cover, 
that is, so that it will burn 0.1 cubic foot of coal gas per hour. Then light 
the gas flame below the bath and adjust to such a height, as determined 
by preliminary tests, that the temperature of the oil will rise at the rate 
of from 4 to 5 deg. F. per minute. For oils flashing above 140 deg. F. 
a bath of cylinder oil flashing above 300 deg. F. is used instead of water. 

Allow the apparatus to stand 10 minutes, to give time for the oil 
vapors to accumulate, meanwhile stirring regularly and constantly at 
one revolution per second, then warm to within 10 deg. F. of the flash 
point and expose the test flame for exactly one second by means of the 
mechanism provided on the cover. Continue stirring and making the 
exposure at each deg. F. rise in the temperature until the flash occurs. 
Particular care must be taken that the cup is not subjected to drafts 
during the test and that the breathing of the operator is not allowed to 
interfere, particularly at the moment the test flame is exposed to the 
vapors. It will be noted that at about 10 deg. F. below the flash point, 
the test flame, as it is exposed to the vapors, will be surrounded by a pale 
blue halo, which gradually increases in intensity until a sudden inflamma- 
tion or gentle explosion of the vapors or the " flash " occurs. The 
temperature at which this occurs, as registered by the thermometer in 
the oil, is the flash point. With fuel oil residues or with poorly refined 
oils from which a small quantity of low-flashing fractions is continually 
being liberated, this halo may first appear as much as 50 deg. F. below 
the flash point. 



TESTING OF LUBRICANTS 403 

The test should always be repeated with a fresh sample. The first 
sample should be thrown away, the cup washed with gasoline, wiped 
dry, and the cup and water bath cooled to the proper temperature. 

This instrument with slight variations in dimensions is the official 
standard in Great Britain, France, Germany, Austria, Denmark, Holland, 
Belgium, Russia, Italy, Norway, Sweden, Japan and is coming into rapidly 
extended use in the United States where it has been recommended by 
government experts for all interstate and foreign trades. 

Doubtless in some places the cost of the Abel-Pensky tester prohibits 
its use. When a high degree of accuracy is not required a simpler type 
of instrument may be used, observing the precautions as stated. The 
open cup should be used for all oils flashing above 250 deg. F. For many 
purposes the flash point and burning points may be determined with 
sufficient accuracy with an open cup tester used in the following manner. 

A glass beaker or metal cup of approximately the same dimensions as 
the Abel-Pensky and Pensky-Martens testers — that is, 5.0 cm. in 
diameter and 5.5 cm. in depth — is filled to within 1.8 cm. of its upper 
rim with the oil to be tested. In testing lamp oils the cup is supported 
in a water bath by a flange at its upper edge, and in testing oils with 
higher flash points, the cup is supported on a sand bath. A thermometer 
is supported with its bulb immersed in the oil. A test-flame burner is 
made by drawing a piece of hard glass tubing to a capillary about 1 mm. 
in diameter, to which gas is supplied. The flame is adjusted to 3 mm. 
cross section. The bath is provided with an ordinary Bunsen burner. 
The method of testing is as nearly as possible like that in official tests 
with the Abel-Pensky tester. 

Open-cup testers such as the Cleveland and the Tagliabur have been 
shown by the Bureau of Mines to give flash-points of lamp oils 8 to 10 
deg. F. higher than the Abel-Pensky instrument described here, and for 
heavy lubricating oils the difference may be as much as 100 deg. F. 
if the special precautions noted here have not been observed. The same 
investigation shows that the Foster reads about 5 degrees higher than the 
Tagliabur closed tester, and that the latter is usually about 15 degrees 
higher than the Elliott tester, and also from 4 to 5 degrees higher than the 
apparatus described. Obviously the tester giving the lowest tests is the 
one most nearly correct if the flame exposure is short in duration and is 
not usually close to the surface of the oil. 

Chill Point. To determine the chill point, pour oil of the kind being 
tested, into a test tube, filling it to a depth of about one-half inch and 
inserting a low-reading (preferably alcohol filled) thermometer. Place the 
test tube in a suitable vessel and pack the test tube in a freezing mixture 
of ice and salt. The vessel should be provided at the bottom with a 
drain which should be open. After the oil has frozen or congealed, the 



404 POWER PLANT TESTING 

chill point is determined by removing the tube from the freezing mixture, 
invert it at an angle of about 60 degrees, and observe the temperature 
indicated by the thermometer when the oil starts to run down the sides 
of the tube. This temperature is the chill point. 

Oil Testing Machines. The type of machine generally used in America, 
for testing an oil to determine its coefficient of friction and its effect in 
preventing undue heating in a bearing, consists of a horizontal steel shaft 
supported on two bearings and with one end overhanging its bearing. 1 
A pendulum is suspended from the overhanging end by a bronze bearing. 
This bearing is made in two halves so as to be easily removable for clean- 
ing and scraping. In order to get results at all comparable on different 
machines the bearing surfaces must be smooth and fit on the shaft as well 
as they can possibly be made. The pendulum is so arranged by means 
of an adjusting screw at the bottom that any pressure applied is trans- 
mitted in its full amount to both halves of the bearing. The adjusting 
screw transmits its pressure on the lower half of the bearing by an inter- 
mediary spring, thus permitting closer adjustments. A pointer on the 
spring indicates on a scale attached to the pendulum the total pressure 
and also the total unit pressure (lbs. per sq. in.) on the two halves of the 
bearing. A thermometer inserted through a hole in the top of the pen- 
dulum, with its bulb resting on the shaft indicates the temperature at 
the bearing surfaces. An iron ball is provided on some of these devices 
to partially counterbalance the weight of the pendulum and thus increase 
its sensitiveness. The deviation of the pendulum from the vertical is 
obviously proportional to the friction. This deflection is measured by 
a pointer moving over a circular arc. If the instrument is in proper 
adjustment the reading on this scale divided by the total pressure exerted 
on the two halves of the bearing is the value of the coefficient of friction. 

Sometimes when the apparatus is to be used at higher pressures than 
the normal spring permits, the spring can be replaced by a stiffer one, 
made of heavier wire. 2 

As the mathematical demonstration is usually stated: 
P = total pressure on the two halves of the journal, lbs. 
p = total unit pressure per sq. in. of projected area on the two halves, 

lbs. per sq. in. 
T = tension in spring, lbs. 

W = gross weight of pendulum, lbs. 
R = effective arm of pendulum, ins. 

1 For a detailed description of slightly different type, (Golden's) see A. L. Westcott 
in the Journal ofA.S.M.E., July, 1913, pages 1143-1167. 

2 The maximum load a spring will carry is proportional to the cube of the diameter 
of the wire. When making a new spring of heavier wire the outside diameter of the coil 
must be made the same as of the normal spring, and the unstressed normal length must 
be the same. 



TESTING OF LUBRICANTS 405 

r = radius of journal, ins. 

a = angle of deflection of pendulum from the vertical. 
F = total force of friction, lbs. 
f = coefficient of friction. 
1 = length of bearing surface. 

Since each half is loaded, the total equivalent projected area is 2 X 
2rl. 

Total load on journal is P = 2 T + W, and 

= JP_ 2T + W 

P 4rl 4rl 

Moment of friction is equal to moment of external forces or, since 

Fr = Pfr = (2 T + W) fr = W'R sin a 

in the case of the friction deflecting the unbalanced weight W of the 
pendulum through the angle a. Then 

_ W'R sin a 
rP 

W'R . 

In any machine of the type described, the term — — is a constant, the 

scale on the arc indicating deflections of the pendulum is usually gradu- 
ated to indicate values of 

r 

As a rule the total and unit pressures stamped on the scale of the 
pendulum type of apparatus are not even nearly correct and it becomes 
necessary to calibrate the spring in the tester, if absolute values are to 
be calculated. This calibration is accomplished most easily by removing 
the brasses from the yoke, taking off the lower part of the pendulum 
which has the thread for tightening up on the spring, and setting up the 
pendulum with the yoke downward in a testing machine for compression 
(page 432) and apply increasing loads on the spring and measure its 
deflection at each point. A stiff bar must be put through the yoke to 
take the pressure from the spring. This bar can be readily supported 
on iron blocks so that the pendulum will be free to move up and down 
with the varying compression on the spring. If all the supporting parts 
are rigid the deflections of the spring can be measured by the distance 
between the head and the base of the testing machine. 

Steam Engine Lubricators. The proper oiling of an engine is most 
important. The operation of nearly all types of lubricating devices 
is easily understood, particularly when operated by the gravity of the 
oil or by a pump. Another type of lubricator for cylinder lubrication 



406 



POWER PLANT TESTING 



which is operated by the weight of a column of condensed steam is 
shown in Fig. 348. The pipe C, in which the condensed steam accumu- 
lates, must be made at least 2 feet long to give a sufficient head or pres- 
sure to feed the oil. The oil reservoir is in the cylindrical vessel below 
the condenser pipe. This is filled with oil through an opening in the 
top as the water which has accumulated in the apparatus is drained 
through the cock D. Water from the condenser pipe C is carried down 
to the bottom of the oil reservoir by the pipe shown in dotted lines 
on the left-hand side. Oil, being lighter than the water, remains in the 





Fig. 348. — Engine Cylinder Lubri- 
cator Operated by Pressure of 
Column of Condensed Steam. 



Fig. 349. — "Detroit" Cylinder 
Lubricator. 



upper part of the reservoir and is forced down through the pipe on the 
right-hand side and through the needle-valve I by which the flow of oil 
can be regulated so that as small an amount as one drop in two or three 
minutes passes into the steam pipe at H to mix with the steam going to 
the engine cylinder. Through the gage glass S the number of drops 
passing through can be observed. Another gage glass L on the side 
of the reservoir shows the relative amounts of oil and water. When 
an engine is not operating all oil cups and lubricators should be care- 
fully closed. The feed of oil from this lubricator is stopped by closing 



TESTING OF LUBRICANTS 407 

the valves V and F. A valve is usually provided on the bulb B, which 
should be closed when draining from D, so that the water in the con- 
denser pipe C will not be lost, and thus prevent the operation of the 
apparatus until a sufficient amount of condensed steam has accumulated 
to produce the pressure necessary to force the oil into the steam pipe. 

A slight modification of the lubricator described is illustrated in Fig. 
349. The condensed steam is brought to the bottom of the reservoir 
through the pipe P, which is open at its lower end. On the other hand, 
the pipe S is open at the top and the oil is forced by the pressure due to 
the head of water in the pipe above (not shown) through the gage glass 
on the left-hand side, then through the horizontal pipe T to which is 
attached the valve and nipple connected to the steam pipe supplying 
the engine. In this figure at the top of the reservoir a plug with a nicely 
finished handle is shown, which is to be removed for filling with oil. 



CHAPTER XXII 



HYDRAULIC MACHINERY 



Tests of Hydraulic Machinery 

Tests of Boiler Feed-pumps. In general engineering practice there 
are two classes of pumps commonly used for " feeding " the water to 
steam boilers. These are: 

(1) Motor- or belt-driven pumps; 

(2) Steam pumps. 

Motor-driven feed-pumps are more generally used in Europe than in 
America, but there are, however, many plants in which feed-pumps 
operated by direct connection to an electric motor or by belting from a 

line shaft are used. Fig. 350 shows 
a good modern example of such a 
pump. It has three plungers oper- 
ated from a single shaft with the 
cranks set 120 degrees apart. The 
valves are accessible for cleaning or 
for repairs by removing the plates 
or " covers " C, C, C. The suction 
pipe is marked S and the discharge 
pipe D. An air-chamber A is pro- 
vided to produce, by cushioning air 
in it, a somewhat more steady flow 
than would be secured without it. 
A relief valve should be provided 
on the discharge pipe to act as a 
safety valve in case the pressure in 
the line should get so high that the 
pump itself might be broken. 
The power delivered to a belt-driven pump can usually be con- 
veniently measured with some type of transmission dynamometer 
(see pages 164-175), while if it is direct-connected to a motor the 
efficiency of the motor may be obtained by disconnecting it, attaching 
a Prony brake to the shaft, and measuring the input to the motor with 
suitable electrical instruments. 

The equivalent work done " on the water " by the pump is found 

408 




Fig. 350. — Belt-driven Feed Pump. 



HYDRAULIC MACHINERY 409 

by multiplying the total head 1 (suction + discharge) in feet by the 
weight of water lifted (foot-pounds). 

The quantity of water delivered can be determined by weighing or 
by calculating the flow over a weir or from an orifice (see pages 201-207) . 

Slip is the difference between the volume swept through by the plunger 
of the pump; or, in general, the piston displacement, and the actual 
volume of the water pumped at the required head. 

In piston pumps, direct-connected to the steam cylinder without a 
crank, the length of the stroke is usually variable, and some special 
method must be adopted for such tests to determine the average length 
of the stroke. 

Duty of a pump is usually defined as the number of foot-pounds of 
work " delivered " by the pump per 1,000,000 B.t.u. supplied. The 
heat units supplied by the engine are calculated by the A.S.M.E. Rules 2 
as the product of the weight of feed-water used by the boiler and the 
total heat of steam at boiler pressure " reckoned from the temperature 
of the feed-water." The total heat is to be corrected of course for 
moisture or superheat. 

For a test utilizing a Webber or a similar dynamometer belted to the 
pump for measuring the power the following form may be used : 

Test op a Belt-deiven Pump 
(Dynamometer Method) 

1. Type of pump Made by 

2. Diameter of plungers, ins 

3. Length of stroke, ft 

4. Size of suction pipe 

5. Size of delivery pipe 

6. Speed of dynamometer, r.p.m 

7. Speed of pump, r.p.m 



1 If the discharge head is measured by a pressure-gage on the discharge pipe then 
the equivalent pressure in pounds per square inch corresponding to the difference in 
level between the surface of the water-supply and the center of the gage must be added 
to get the total head. (One foot-head of water at about 62 degrees Fahrenheit is equiv- 
alent to 0.434 pound per square inch; and conversely, one pound per square inch is 
equivalent to a head of 2.305 feet of water at the above temperature.) 

This is usually stated as the vertical distance between the two gages. A vacuum 
gage, however, on the suction pipe of a pump indicates the vacuum at the level of the 
top of the suction pipe, and not up to the center of the gage. This was shown by Pro- 
fessor Cooley by attaching a gage by means of a suitable fitting to the suction pipe 
of a pump so that the gage could be revolved above and below the pipe. It was ob- 
served that the reading of the gage remained constant, showing that in a suction pipe 
of a pump the water does not rise higher than the top of the pipe. 

2 More detailed instructions for steam pumps with steam jackets are given in Trans- 
actions American Society of Mechanical Engineers, vol. 12, page 530. 



410 



POWER PLANT TESTING 



8. Dynamometer reading 

9. Delivery pressure, lbs. per sq. in 

10. Suction pressure, lbs. per sq., in. or inches vacuum 

11. Temperature of water, deg. F 

12. Delivery head in feet of water 

13. Suction head in feet of water 

14. Total head in feet of water 

15. Net weight of water pumped per minute, lbs 

16. Work done by pump, ft.-lbs. per min. (14) X (15) 

17. Cubic feet water pumped per minute 

18. Plunger displacement, cu. ft. per min 

19. Slip, per cent [(18) - (17)] -=- (18) 

20. Net work delivered to pump (by dynamometer) ft.-lbs. per minute 

21. Dynamometer horse power (20) 4- 33,000 

22. Pump horse power (16) -H 33,000 

23. Mechanical efficiency (22) -f- (21) 

24. Capacity of pump, gallons delivered per 24 hours 

A Direct-acting Steam Feed-pump like the one shown in section in 
Fig. 351 will be tested in a somewhat different manner, and a different 
set of observations is required. 

In none of the so-called direct-acting steam pumps has a rotary motion 
been developed by means of which an eccentric can be made to operate 




Direct-acting Steam Pump. 



the valve. It is, therefore, necessary to reverse the piston by an im- 
pulse derived from itself at the end of each stroke. This cannot be 
effected in an ordinary single-valve engine, as the valve would be moved 
only to the center of its motion, and then the whole machine would 
stop. To overcome this difficulty a small steam piston is provided to 
move the main valve of the engine. 

In these pumps the lever A, which is carried by the piston rod, comes 
in contact with the tappit when near the end of its motion, and by means 
of the valve rod R moves the small slide valve which operates the supple- 
mental piston. The supplemental piston, carrying with it the main valve 
V, is thus driven over by steam, and the engine is reversed. If, however, 



HYDRAULIC MACHINERY 



411 



the supplemental piston fails accidentally to be moved, or to be moved 
with sufficient promptness by steam, the lug on the valve rod engages 
with it and compels its motion by power derived from the main engine. 
Outside-packed steam pumps of the plunger type (Fig. 352) are now 
very commonly used for supplying boiler feed-water, chiefly because at 
the pump end the only part subjected to ordinary wear is the packing of 




Outside Packed Plunger Feed-pump. 



the plunger stuffing-boxes. Steam is admitted at A and exhausts at E. 
The suction pipe is at S and the discharge pipe at D. 

Suitable fittings for the attachment of indicators should be provided 
at both the steam and the water cylinders. ' If the pump is of the ordi- 
nary direct-connected type, without a flywheel, like the one shown in 
Fig- 35 1 ? some provision must be made to make regular observations of 




Fig. 353. — Cooley Stroke-measuring Device. 

the length of the stroke, as it is scarcely ever constant. One method is 
to attach a suitable arm to the cross-head H, Fig. 351, with a pencil at 
the end. Strips of tough paper can then be pasted on a board in such a 
position that the pencil will trace the lengths of the strokes. By shifting 
the position of the board every minute or two, records will be obtained 
from which the average length of the stroke can be estimated with con- 
siderable accuracy. 



412 



POWER PLANT TESTING 



Cooley Stroke Measuring Device. 1 Another method giving still 
greater accuracy is to use a counting device designed by Professor Cooley, 
operated by a mechanism similar to that in a clock (Fig. 353). A cord 
from the instrument is attached to the cross-head of the pump and the 
clock mechanism moved by this cord integrates or sums the lengths of all 
the strokes. This apparatus has been developed for measuring accurately 
the length of the stroke of the type of pumps in which steam and water 
cylinders are direct-connected on the same piston rod, such for example 
as the ordinary steam feed-pumps. In such pumps it scarcely ever 
happens that there are two strokes in succession that are of the same 
length and more or less approximate methods are usually adopted 




Fig. 354. — Mechanism of Stroke-measuring Device. 

for obtaining the average length of the stroke during a test. With 
the stroke-measuring device referred to above each individual stroke 
is accurately measured and is added by a counting device to the sum 
of all the other strokes that have preceded. As this apparatus is used in 
a test of a variable stroke pump, the reading of the counter to the nearest 
inch can be recorded at the usual times for observations. The dif- 
ference between two readings is the total length of all the strokes for 
the interval between observations. If, then, this difference is divided 
by the total number of strokes for the same time, the average length of 
the stroke can be determined accurately. An assembled view of this 
device is shown in Fig. 353, and its mechanism is shown in Fig. 354, which 
it will be observed is the same in principle as the silent ratchet clutches 
used for the continuous indicator described on page 106. The apparatus 
1 Made by Engineering Shops, Ann Arbor, Mich. 



HYDRAULIC MACHINERY 413 

is driven by the cord on the wheel W, which moves the ratchet wheels 
B and C in the same way as the corresponding parts are moved in the 
continuous indicator referred to. Numbers on the horizontal plate 
(Fig. 353) are feet and those on the circular dial are inches. 

RULES FOR CONDUCTING DUTY TRIALS OF STEAM PUMP- 
ING MACHINERY. 1 A.S.M.E. CODE OF 1912 

Read the general instructions given on pages 258 to 266. Determine 
the object, take the dimensions, note the physical conditions not only 
of the pumping machinery but of all parts of the plant concerned, examine 
for leakages, install the testing appliances, etc., as there pointed out, 
and prepare for the test accordingly. 

In a reciprocating pump determine the quantity of water leakage or 
slip past the plungers, and that of the pump valves, if any, as explained 
on pages 409 and 414. 

The apparatus and instruments required for a simple duty trial of 
pumping machinery, in which the steam consumption is determined by 
feed water measurement, are: 

(a) Tanks and platform scales for weighing water (or water meters calibrated in 

place). 
(6) Graduated scales attached to the water glasses of the boilers. 

(c) Pressure gages, vacuum gages, and thermometers. 

(d) A steam calorimeter. 

(e) A barometer. 

(/) A tachometer or other speed-measuring apparatus. 

(g) For rotary pumps a weir or other means for measuring the quantity of water 

pumped. 
(h) Stroke scales or measuring devices, for direct-acting pumps. 

In trials of a reciprocating pumping engine, involving the determina- 
tion of the complete performance, the weir or other means of measure- 
ment noted should be provided, and in addition the following: 

(i) Steam-engine indicators. 
0') A planimeter. 

The steam consumed by steam-driven auxiliaries which are required 
in the operation of the pumping machinery should be included in the 
total steam from which the heat consumption is calculated, the same as 
noted in the Steam Engine Code. 

In trials for maximum duty care should be taken that no air is snifted 
into the pump cylinders, causing imperfect filling. In such cases, and 
indeed in all cases where air is thus admitted in sufficient quantity to 

1 In the case of a pump driven by some other prime mover than a steam engine or 
steam turbine, the code may be modified to suit the particular circumstances. 



414 POWER PLANT TESTING 

affect the performance as revealed by indicator diagrams from the water 
end, the result should be corrected accordingly. 

The rules pertaining to the subjects Duration, Starting and Stopping, 
and Records are identically the same as those given under the respective 
headings in the Steam Engine Code, pages 294 and 296, and reference 
may be made to that code for the necessary directions in these particulars. 
Where the pump-end is of the reciprocating class, the indicator diagrams 
should be taken not only from the steam cylinders but also from the 
water cylinders. 

Water Horse Power. The water horse power in a reciprocating pump is found 
by multiplying the net area of the plunger in sq. in. by the total head, which is 
made up of the pressure shown by the gage on the force main, that on the suc- 
tion main, and that representing the vertical distance between the centers of the 
two gages, all expressed in lb. per sq. in.; the length of the stroke in ft.; and 
the number of single strokes per minute; and dividing the final product by 
33,000. 

In a rotary pump the water horse power is found by multiplying the weight 
of water discharged per hour in lbs., as determined by weir or other measure- 
ment; by the total head in ft., as determined from the readings of the gage on 
the force main, that on the suction main, and the vertical distance between 
the two gages; and the product divided by 1, 980,000.* 

Duty. The duty per million heat units is found by dividing the number of 
ft.-lbs. of work done during the trial by the total number of heat units consumed; 
and multiplying the quotient by 1 ; 000,000. The amount of work is found in 
the case of reciprocating pumps by multiplying the net area of the plunger in 
sq. in., the total head expressed in lb. per sq. in. (which is made up of the pressure 
shown by the gage on the force main, that on the suction main, and the vertical 
distance between the centers of the two gages, all reduced to lbs.), by the length 
of the stroke in ft., and the total number of single strokes during the trial; 
finally correcting for the percentage of leakage of the pump. In a rotary pump 
the work done is found by multiplying the weight of water discharged during 
the trial, as determined by weir or other measurement, by the total head in ft. 

The duty per 1000 lb. of dry steam is found by dividing the ft.-lbs. of work 
done, as noted, by the total weight of dry steam, and multiplying the quotient 
by 1000. 

Capacity. The capacity in gal. per 24 hrs. for reciprocating pumps is found 
by multiplying the net area of the plunger by the length of the stroke in ft. (in 
direct-connecting engines the average length of stroke) ; then by the number of 
single strokes per minute; and the product of these three by the constant 74.8; 
finally correcting for the percentage of leakage of the pump. 

Leakage of Pump. The percentage of leakage is the percentage borne by the 
quantity of leakage found on the leakage trial, to the quantity of water dis- 
charged on the duty run determined from plunger displacement. 

Friction. The percentage of total friction in a reciprocating pump is the 
percentage borne by the friction horse power to the indicated horse power of 
the steam cylinders. 

1 If there is a material difference in velocity of the water at the points where the 
gages are attached, a correction should be made by the corresponding difference in 
"velocity head." 



HYDRAULIC MACHINERY 415 

Miscellaneous. For the calculation of other results pertaining specially to 
the performance of the steam end of a reciprocating pump, reference may be 
made to the Steam Engine Code. 

DATA AND RESULTS OF DUTY -TRIAL OF STEAM PUMPING MACHINERY 
CODE OF 1912 

(1) Test of pump, located at 

to determine conducted by 

(2) Type of machinery 

(3) Rated capacity in gals, per 24 hrs : 

(4) Type of boiler 

(5) Type of auxiliaries 

(6) Dimensions of engine or turbine 

(7) Dimensions of pump ; 

(8) Dimensions of boilers 

(9) Dimensions of auxiliaries . 

(10) Dimensions of condenser 

(11) Date. 

(12) Duration hrs. 

Average Pressures and Temperatures 

(13) Steam pressure at boiler by gage lbs. per sq. in. 

(14) Steam pipe pressure near throttle, by gage lbs. per sq. in. 

(15) Barometric pressure of atmosphere in ins. of mercury ins. 

(16) Pressure in receiver by gage lbs. per sq. in. 

(17) Vacuum in condenser in ins. of mercury ins. 

(18) Pressure in force main by gage lbs. per sq. in. 

(19) Pressure in suction main by gage lbs. per sq. in. 

(20) Vertical distance between centers of two gages ft. 

(21) Total head, expressed in lbs. pressure lbs. per sq. in. 

(22) Total head, expressed in ft ft. 

(23) Temperature of main supply of feedwater to boilers deg. F. 

(24) Temperature of additional supplies of feedwater deg. F. 

(25) Temperature of air in engine room deg. F. 

Total Quantities 

(26) Water fed to boilers from main source of supply . . . lbs. 

(27) Water fed from additional supplies lbs. 

(28) Total water fed to boilers from all sources lbs. 

(29) Moisture in steam or superheating near throttle per cent or deg. F. 

(30) Factor of correction for quality of steam, dry steam being unity 

(31) Total dry steam consumed for all purposes lbs. 

(32) Total leakage of plungers and valves gals. 

(33) Total number of gallons of water discharged: 

(a) By plunger displacement, uncorrected gals. 

(b) By plunger displacement, corrected for leakage gals. 

(c) By weir or other measurement of discharge gals. 

(34) Total weight of water discharged: 

(a) By plunger displacement, corrected lbs. 

(b) By measurement of discharge. » . — lbs. 



416 POWER PLANT TESTING 

Hourly Quantities 

(35) Water fed from main source of supply lbs. 

(36) Water fed from additional supplies lbs. 

(37) Total water fed to boilers per hour lbs. 

(38) Total dry steam consumed per hour lbs. 

(39) Loss of steam and water per hour due to drips from main steam pipes and 

to leakage of plant lbs. 

(40) Net dry steam consumed per hour lbs. 

(41) Dry steam consumed per hour: 

(a) By main engine or turbine lbs. 

(6) By auxiliaries lbs. 

(42) Water discharged per hour: 

(a) By plunger displacement, corrected lbs. 

(b) By measurement of discharge lbs. 

Heat Data 

(43) Heat units per lb. of dry steam based on temperature, Line 23 B.t.u. 

(44) Heat units per lb. of dry steam based on temperature, Line 24 B.'t.u. 

(45) Heat units consumed per hour based on main supply of feed B.t.u. 

(46) Heat units consumed per hour based on additional supplies of feed B.t.u. 

(47) Total heat units consumed per hour for all purposes B.t.u. 

(48) Loss of heat per hour due to leakage of plant, drips, etc B.t.u. 

(49) Net heat units consumed per hour B.t.u. 

(50) Heat units consumed per hour: 

(a) By engine or turbine alone ' B.t.u. 

(6) By auxiliaries B.t.u. 

Indicator Diagrams 

(51) Mean effective pressure lbs. per sq. in. 

Speed and Stroke 

(52) Revolutions per minute 

(53) Number of single strokes per minute 

(54) Average length of stroke ft. 

Power 

(55) Indicated horse power developed: 

1st cylinder i.h.p. 

2d cylinder i.h.p. 

Whole engine i.h.p. 

(56) Water horse power h.p. 

(57) Friction h.p. (Line 55 — Line 56) fr. h.p. 

(58) Percentage of i.h.p. lost in friction per cent 

Duty 

(59) Duty per million heat units ft.-lbs. 

(60) Duty per thousand lb. of steam ft.-lbs. 

Work Done per Heat Unit 

(61) Ft.-lbs. of work per B.t.u. (Line 59 -f- 1,000,000) ft.-lbs. 



HYDRAULIC MACHINERY 417 

Capacity 

(62) Number of gals, of water pumped in 24 hrs.: 

(a) By plunger displacement, corrected for leakage gals. 

(6) By weir or other measurement gals. 

(63) Gallons of water per minute: 

(a) By plunger displacement, corrected for leakage gals. 

(b) By weir or other measurement gals. 

Economy Results, Steam End 

(64) Heat units consumed per i.h.p. per hour: 1 

(a) By engine and auxiliaries B.t.u. 

(6) By engine alone B.t.u. 

(c) By auxiliaries B.t.u. 

(65) Dry steam consumed per i.h.p. per hour: 

(a) By engine and auxiliaries lbs. 

(6) By engine alone lbs. 

(c) By auxiliaries lbs. 

RULES FOR CONDUCTING TESTS OF COMPLETE STEAM 
PUMPING MACHINERY PLANTS 

Object and Preparations 

This code applies to a commercial test of a complete steam pumping 
machinery plant, having for an object the determination of the fuel cost 
of pumping a given quantity of water for a day's run of 24 hours. For 
tests of the component parts of the plant, rules may be found in the 
respective codes applying thereto. 

Determine the character of the fuel to conform with the object in view. 
To obtain maximum economy or capacity, the fuel should be some kind 
of coal that is regarded as a standard, as noted in the Boiler Code, 
page 269. 

The duration of a test of a complete pumping machinery plant should 
be not less than one day of 24 hours. 

In cases where the machinery is in operation only a part of the calender 
day, the coal consumption used in computing the results should be that 
of the entire 24 hours. 

The methods of starting and stopping a test of a complete pumping 
plant, sampling and drying coal, determining ashes and refuse, and 
ascertaining the calorific value and chemical analysis of the coal are the 
same as those described in the Code for Complete Steam Power Plants, 
pages 231 and 337. 

For the calculation of water horse power, duty, capacity, and leakage 
of pump reference may be made to the explanations given on pages 
413 and 414 of the Pumping Engine Code. 

1 The i.h.p. on which the economy results are based is that of the main engine given 
in Line 54. 



418 POWER PLANT TESTING 



DATA AND RESULTS OF TEST OF STEAM PUMPING MACHINERY PLANT 
CODE OF 1912 

(1) Test of plant located at 

to determine conducted by 

(2) Type of machinery 

(3) Rated capacity in gallons per 24 hrs 

(4) Type of boilers 

(5) Type of auxiliaries 

(6) Dimensions of machinery 

(7) Dimensions of boilers 

(8) Dimensions of auxiliaries 

(9) Dimensions of condenser 

(10) Date 

(11) Duration hrs 

(12) Length of time machinery was in motion with throttle open hrs. 

(13) Length of time machinery was running at normal speed , .hrs. 

Average Pressures and Temperatures 

(14) Steam pressure at boiler by gage lbs. per sq. in. 

(15) Pressure in force main by gage lbs. per. sq. in. 

(16) Pressure in suction main by gage ins. mercury 

(17) Vertical distance between centers of two gages ft. 

(18) Total head expressed in lbs. pressure lbs. per. sq. in. 

(19) Total head expressed in ft ft. 

Speed and Stroke 

(20) Revolutions per minute 

(21) Number of single strokes per minute 

(22) Average length of stroke ft. 

Total, Quantities 

(23) Total coal as fired lbs. 

(24) Moisture in coal per cent 

(25) Total dry coal consumed lbs. 

(26) Ash and refuse lbs . 

(27) Percentage of ash and refuse to dry coal per cent 

(28) Calorific value per lb. of dry coal by calorimeter test B.t.u 

(29) Cost of coal per ton of ... . lbs dollars 

(30) Total leakage of plungers and valves gals 

(31) Total number of gals, of water discharged: 

(a) By plunger displacement, uncorrected gals. 

(6) By plunger displacement, corrected for leakage gals. 

(c) By weir or other measurement gals. 

Hourly Quantities 

(32) Dry coal consumed per hour, based on duration of running period (Line 

25 + Line 12) lbs. 



HYDRAULIC MACHINERY 



419 



Power 

(33) Water horse power h.p. 

Economy Results 

(34) Dry coal consumed per water h.p. per hour lbs. 

(35) Cost of coal per water h.p. per hour cents 

(36) Duty per 100 lbs. of dry coal 

Capacity 

(37) Number of gals, of water pumped in 24 hrs.: 

(a) By plunger displacement, corrected for leakage gals. 

(6) By weir or other measurement gals. 

(38) Number of gals, of water pumped per minute: 

(a) By plunger displacement, corrected for leakage gals. 

(b) By weir or other measurement gals. 

Tests of Centrifugal Pumps. Tests of pumps operating against 
low heads such as single-stage centrifugal pumps are made in the same 
way as explained, for the triplex belt-driven feed-pump. It is desired, 
of course, from the results of the tests to compare the power supplied to 
the pump with the work done in lifting the water. Power supplied would 
probably be again measured by some 
form of transmission dynamometer, 
and the work done is calculated from - , 

the weight of water delivered and the 
total head against which the pump 
delivers. 1 

Centrifugal pumps are frequently IP 
driven by direct-connected steam tur- 
bines. The horse power required to 
drive the pump is then determined ! 
from a speed-power curve similar to 
the turbine (Fig. 308), page 316, ob- 
tained usually from a Prony brake 
test of the turbine. Similarly, if the 
pump is driven by a variable-speed 
electric motor, a speed-power curve '■• y Mm WW 

of the motor can bo used. Usually, JMwMr 

however, when a constant speed motor «?8Sp^ 

is used it is simpler to determine an FlG> 355.- Bucket of an Impulse Water 
efficiency curve of the motor for vary- Wheel, 

ing power. 

Tests of Impulse Water Wheels. Impulse wheels used to operate with 
water under pressure consist usually of a series of buckets attached to 

1 For more detailed testing of centrifugal pumps see "Centrifugal Pumps," by 
Lowenstein and Crissey (D. Van Nostrand Co., 1911). 




420 



POWER PLANT TESTING 




Fig. 356. — Typical Impulse Water Wheel. 




Fig. 357. — Water Jet Discharging at High Pressure from the Nozzle of an Impulse 

Wheel. 



HYDRAULIC MACHINERY 421 

the periphery of a disk or wheel. The buckets are usually divided by 
a central rib so that two " pockets " are formed (Fig. 355). The curves 
for each of the divisions of the bucket are designed to turn the direction of 
the impinging steam without shock. Fig. 356 shows a typical impulse 
wheel. Impulse wheels are designed to operate most efficiently with 
high heads. It is, therefore, impracticable to measure the head directly 
in feet, but it is done usually by measuring the pressure near the nozzle 
N with a gage. When the center of the gage is at a higher level than 
the center of the nozzle discharging on the wheel, then this difference 
in level must be added to the head calculated from the gage pressure 
to determine the total head under which the wheel is operating. Power 
developed is measured usually by a Prony brake connected to the shaft 




Fig. 358. — Buckets and Jet of a Pelton Wheel. 

S. In all tests where a large quantity of water is used, the temperature 
of the water should be recorded and the weight corresponding should 
be used. A view of the jet discharged from one of these nozzles is given 
in Fig. 357. The type of impulse wheel most in use commercially is 
called the Pelton, of which typical buckets and the engaging jet of 
water are shown in Fig. 358. 

Laboratory tests for a given head are usually run when varying both 
the load and speed. Make the first test with the load on the Prony 
brake as light as possible consistent with fairly steady operation of the 
wheel, and then take a series of tests increasing the load in increments 
to reduce the speed about 100 revolutions per minute in each succeeding 
test. Duration of test at each speed should be from twenty to thirty 
minutes with observations taken every two minutes. The following 
form may be used for tests: 



422 POWER PLANT TESTING 

Test op Impulse Wheel 
General Data: 

1. Date : 

2. Name of wheel and nominal horse power 

3. Kind of bucket 

4. No. of buckets 

5. Angle of buckets 

6. Diameter of bucket wheel, inches 

7. Area of nozzle and delivery pipe, sq. ins 

8. Coefficient of discharge for type of nozzle 

9. Diameter of brake wheel, inches . 

10.. Length of brake arm, inches 

11. Tare of brake, lbs 

12. Duration of test 

13. Average temperature of water, deg. F 

14. Average pressure by gage at wheel, lbs. per sq. in 

15. Average head at wheel in feet 1 

16. Quantity of water for total run in pounds 

17. Quantity of water in pounds per minute 

18. Cubic feet of water per minute 

19. Foot-pounds of work per minute calculated from (15) and (17) 

20. r.p.m 

21. Net weight on brake, lbs 

22. Horse power as measured by brake 

23. Over-all efficiency of motor, per cent (22) -h (19) X 33,000 

Curves. Plot a curve for each head with speed for abscissas and 
efficiency per cent for ordinates, also curves for the ratio of the velocity 
of the periphery of the wheel v p to the theoretical velocity due to the 
head v«; that is, v p /v t for abscissas and the maximum horse power 
developed for ordinates. 2 

Tests of Water Turbines. A typical reaction turbine is shown in 
Fig. 359» The power is transmitted by the main shaft and the smaller 
shaft is used for controlling the gates regulating the quantity of water 
passing through the wheel. For testing a Prony brake can be placed 
directly on the vertical shaft. In some respects a rope brake is most 
suitable, as one end can be attached to a spring balance and the other 
end can be led over a pulley, and will thus support weights on a vertical 
hanger. It is preferable to have the lower web of the brake-wheel 
solid, that is, without arms, so that it will retain the cooling water, 
which should be arranged to flow into it at the rate required. 

Power supplied is determined by the weight of water used and by 
the head under which the wheel operates. These quantities are deter- 

1 Corrected for vertical distance from the center of the gage to the center of the 
nozzle. 

2 Plot curves showing effect of head on efficiency if several tests are run at differ- 
ent heads. 



HYDRAULIC MACHINERY 



423 



mined in the same general way as for a test of an impulse wheel, already 
described, except in the case of a reaction turbine, where the housing 
or casing in which the wheel is placed is always completely filled with 
water. With this arrangement the turbine receives not only the effect 
due to the pressure-head, measured from the level in the head-race 
to the center of the wheel, but also that due to the suction head, measured 
from the center of the wheel to the level in the tailrace. Data can be 
recorded in a form similar to that for tests on impulse wheels. 




Typical Reaction Water Turbine.' 



Curves. Plot a curve for each gate opening at a constant head with 
speed for abscissas and efficiency per cent for ordinates. 

Air Lifts. Pumping water by compressed air has had in recent years 
extensive application. There are several methods in use, but the most 
successful is that using air expansively for raising water as shown diagram- 
matically in Fig. 360, called the " Air lift." It consists of a delivery- 
pipe D set down into the well and a smaller pipe for compressed air 



424 



POWER PLANT TESTING 



having a nozzle N at the end and entering the discharge pipe as shown. 
It is a more usual construction to admit the air to the discharge pipe 
through holes from an annular chamber encircling it, but the method 

of operation is practically the same as 
shown. Water is raised by the buoyancy 
of the air. Let hi be the depth of sub- 
mersion of the delivery pipe measured to 
the point where the air enters, and h 2 be 
the total lift measured from the same 
point. Pressure of air at the place of 
entrance must be theoretically equal to 
the pressure corresponding to the head of 
mixed water and air above it in D. This 
pressure decreases, however, as the air 
rises and expands so that at the top of D 
the pressure is little above atmospheric. 
Work required of the compressor varies 
with the difference between the depth of 
submersion of the delivery pipe hi com- 
pared with the net lift h 2 — hi. The pres- 
sure required is then comparatively high 
and the efficiency low. On the other hand, 
a very small submergence necessitates a 
relatively large quantity of air to produce 
the required velocity, so that again the efficiency is low. Maximum 
efficiency, usually about 50 per cent, is obtained when the net head h 2 
— hi is from 15 to 30 feet. At 150 feet the efficiency is scarcely ever as 
much as 20 per cent. 

The following quantities should be determined in a test: (1) horse 
power of air compressor ; (2) volume of free air (see page 376, line 72) 
compressed; (3) weight of water pumped; (4) net lift (h 2 — hi); (5) 
efficiency, which is the ratio of the work equivalent of lifting the water 
to the work done in compressing the air, both in foot-pound units. 

Tests of Hydraulic Rams. A section of a typical hydraulic ram is 
shown in Fig. 362. It consists of an air chamber H, to which is connected 
the discharge pipe I. There is a check valve G opening into the air 
chamber from the lower chamber A into which water is brought by the 
pipe S. There is a waste valve at B. This valve is weighted and opens 
inward. By means of a nut J on the stem of this valve the lift or amount 
of opening of the valve can be regulated. When water is supplied to the 
ram, it escapes through the waste valve B with a velocity corresponding 
approximately to that due to the head under which the water is supplied. 
The effect of this velocity head is to reduce the pressure on the upper side 




Fig. 360. — Air Lift. 



HYDRAULIC MACHINERY 



425 



of the valve so that it becomes unbalanced and closes suddenly. Then 
the momentum of the column of water in the pipe S becomes sufficient 
to open the valve G, and will discharge some water into the discharge 
pipe I against a considerable head. As soon as the pressures become 
equalized the valve G closes, the waste valve B opens and water from the 
supply pipe is again " wasted." This alternate action is produced with 
regularity, and as a result the water in the supply pipe acquires a certain 
" backward and forward " wave-motion. As the rule is generally stated, 
the length of the supply pipe leading from the reservoir to the ram must 
be at least five times the head. This length is necessary to secure some 
resistance to this " backward and forward " wave-motion. A small air 
chamber shown at P, with a check-valve C opening inward to supply air, 




Fig. 362. — Section of a Simple Hydraulic Ram. 

is provided in many of these rams, as it improves the efficiency. The 
rate of opening of the waste valve or the number of pulsations in a given 
time can be varied by changing the weight on its stem. This apparatus 
is tested usually by measuring the supply and the discharge heads, the 
weight of water discharged through the delivery pipe Wi and that passing 
through the waste valve w 2 in pounds per minute. Then the available 
energy in the water is (wi + w 2 )h s , where h s is the supply head; and the 
useful work is Wih d , where h d is the discharge head, 1 then, 

Efficiency = 7 — * lhd . . , (131) 

(wi + w 2 ) h s 

and the capacity Q in gallons per twenty-four hours is Q = 1440 w x q, 
where q is the fraction of a gallon of water in a pound. Satisfactory runs 
of twenty minutes' duration can usually be made, each run being made 

1 Both the supply and the discharge heads must be measured, of course, from the 
same datum or "zero" level. 



426 



POWER PLANT TESTING 



with a different lift or " stroke " of the waste valve B. Observations 
of the heads should be taken every five minutes if they are variable, and 
weighing as often as necessary, depending on the size of the tanks used. 
The effect on the efficiency of increasing the lift or " stroke " of the waste 
valve from one-eighth inch by increments of one-eighth inch is very 
interesting. 

Curves. Plot curves with length of " stroke " as abscissas and take 
for ordinates: 

(1) Efficiency; 

(2) Capacity in gallons per twenty-four hours; • 

(3) Strokes per minute. 

Fig. 363 shows a slightly different form of ram, as made commercially. 
The principle of operation is, however, the same as the one in Fig. 362. 
Letters used for marking the parts are the same in the two figures. 

Tests of Pulsometers. A type of steam pump called a pulsometer is 
illustrated in section in Fig. 365. In the form shown here it consists of 





Fig. 363. — Commercial Type 
of Hydraulic Ram. 



Fig. 365. — Steam Pulsometer. 



two chambers AA, joined by tapering necks into which a ball C is fitted 
so as to move in the direction of the least pressure between seats in these 
tapering passages. The chambers AA, on opposite sides, are connected 
by means of check or clack valves EE with the " induction " chamber D. 
Water is delivered through the passage H, which is connected "to the 
chambers through the valves G. Between the chambers is also a vacuum 



HYDRAULIC MACHINERY 427 

chamber J, connecting them, with the " induction " chamber D. Small 
air valves, moving inward, supply air to the chambers AA by opening 
when the pressure is less than atmospheric. Its operation is explained 
briefly as follows: Starting with the left-hand chamber full of water and 
with a vacuum in the right-hand chamber, this latter chamber will fill 
with water which by its momentum due to rushing in suddenly, pushes 
back the valve C toward the left. Now during this time steam has 
entered the left-hand chamber to the left of the valve C (before it has 
shifted) and by exerting a pressure on the surface of the water it forces 
it through the check valve G, first into the delivery passage H and then 
into the air chamber J. Then the steam in this left-hand chamber con- 
denses in contact with the cold water and forms a vacuum, permitting 
the repetition of this cycle of events, except that the operations in the 
two chambers are reversed. 

Since all the steam used is condensed and discharged with the water 
lifted, the analysis of the operations in a pulsometer are similar to those 
in the familiar types of injectors, except that the steam acts in the 
pulsometer by pressure instead of by impact as in the injector. 

Using the following symbols: 

w a = weight of dry steam, pounds; 
w„, = weight of water lifted, pounds; 

ti = temperature of the water supply, deg. Fahr.; 

t 2 = temperature of the water delivered, deg. Fahr.; 

r = the latent head of evaporation of the steam in B.t.u.; 

t 8 = the temperature of the steam, deg. Fahr.; 
hi = the suction head, feet; 
h 2 = the delivery head, feet; 
hi + h 2 = the total head, feet, then 

w 8 (t 8 - t 2 + r) = w w (f 2 - ti) (132) 

The heat equivalent of the mechanical work done is in B.t.u., 

r^g (w»hi + (w. + w„) hi), 

and the heat expended is in B.t.u., 

w 8 (t s - t 2 + r), 
and 

Thennal Efficiency - £££ I*?* . • • (US) 

And if we neglect the work done in lifting the condensed steam, 

Efficiency = ^±^j d34) 



428 



POWER PLANT TESTING 



Curves. Plot with discharge pressures for abscissas curves with both 
thermal efficiency and capacity (gallons or pounds of water per twenty- 
four hours) as ordinates. 

Tests of Injectors. The injector is known particularly in stationary 
service as the device used for pumping water into the boiler when the 

' feed-pump fails. One of the 

various forms of injectors sold 
commercially is shown in Fig. 
366. The steam supply, the suc- 
tion or water supply, the delivery 
or discharge, and the overflow are 
marked clearly. 

Method of Operating Injec- 
tors. The method to be given, 
although applicable particularly 
to the ones described, is, how- 
ever, more or less generally ap- 
plicable to all makes. Open wide 
both the steam- and water-sup- 
ply (suction) valves. Then close 
the water-supply (suction) valve 
slowly until the overflow ceases. 
Regulate the rate of delivery 
by closing the water-supply (suc- 
tion) valve. Before testing an 
injector or indeed even before 
trying to operate a new injector, 
inspect the pipe fittings and particularly the valves on the water-supply 
pipe to observe whether they are tight. It is not at all unusual to find 
that the valve is not air-tight, and for this reason it is a very good prac- 
tice to put always some new wicking in the space for packing around the 
stem of the valve on the water-supply pipe; and turn up the cap over 
the packing tightly. 

Method of Testing. For the testing of injectors the arrangement of 
apparatus consists usually of two barrels supported on platform scales, 
or carefully calibrated tanks fitted with gage glasses. During a test the 
injector draws water from one barrel or tank and discharges it into the 
other. A test of an injector must be made, of course, with established 
conditions; that is, with a flying start. This may be accomplished by 
having the injector draw water from the supply tank, but discharge water 
through a by-pass connection on the discharge pipe until the test is to 
begin. For this preliminary operation of the injector the level in the 
supply tank can be maintained very closely, at any point marked by 




— Single Tube Steam Injector. 



HYDRAULIC MACHINERY 429 

manipulating a " quick-opening " valve. When the test is to begin, close 
as quickly as possible this valve on the pipe discharging into the supply 
tank and turn the discharge from the by-pass into the delivery tank. 
To make this adjustment all the valves to be operated should be of the 
" quick-opening " type. The pressure against which the injector is to 
operate is secured by throttling the discharge pipe by means of a globe 
or an angle valve placed between the injector and the by-pass on the 
discharge pipe. The quick-opening valve would not be satisfactory. 
The suction head is measured from the middle of the injector to the 
average level of the water in the supply tank. The discharge head is 
obtained by adding to the head in feet corresponding to the pressure 
indicated by the gage the distance in feet from the center of the gage to 
a horizontal line through the middle of the injector. The temperatures 
of the water in the supply and delivery pipes must be observed. The 
injector is stopped at the end of the test by closing the steam valve. 

The following form, similar to the one used at Purdue University, is 
very complete. Notes explaining the calculations required are given 
above : 

Test of an Injector 

Make of injector Date 

Number 

Size of connections: steam in. dia.; water in. dia.; discharge 

in. dia.; area of discharge ( = a) sq. in. 

Diameter (minimum) of lifting tube in.; forcing tube in. 

a. Duration of test 

b. Steam pressure (average) pounds gage, p s 

c. Delivery pressure (average) pounds gage, p 2 

d. Maximum pressure against which injector will discharge, p max 

e. Suction-head (average), feet, hi 

/. Delivery-head (average), feet, h 2 

g. Temperature of supply (average) fa 

h. Temperature of delivery (average) fa 

i. Pounds water supplied per hour, w w 

j. Pounds water and steam delivered per hour, w m 

k. Cubic feet of water delivered per hour, Q 

1. Wet steam per hour, w s ( = w m — w w ) 

m. Dry steam per hour, w' s ( = xw s ) 

n. Water delivered per pound wet steam, pounds ( = w w -f- w s ) 

o. Water delivered per pound dry steam, pounds ( = w w -f- w' s ) 

p. Velocity of discharge, feet per second, v ( = 144 Q -f- 3600 a) 

q. Energy delivered, raising injection water, B.t.u. per hour 

r. Energy delivered, heating injection water, B.t.u. per hour 

s. Energy delivered, velocity of discharge, B.t.u. per hour 

t. Total energy delivered, B.t.u. per hour 

u. Energy supplied, B.t.u. per hour 

v. Thermal efficiency as a boiler-feed apparatus 

w. Thermal efficiency as a pump 



430 POWER PLANT TESTING 

x. Horse power 

y. Dry steam per horse power per hour, pounds 

The energy of raising injection water = [w w (hi -+- h 2 ) + w g h 2 ] -f- 778 B.t.u. per hour. 
The energy of heating injection water = w w (q 2 — qi) where qi and q 2 correspond to h 

and U B.t.u. per hour. 
The energy of discharge = w m v 2 -f- (2 g X 778) B.t.u. per hour. 
The total energy delivered = item q + item r + item s. 
The energy supplied = w s (xr s + q s — q 2 )i where r 3 and g s correspond to p 8 , and g 2 

corresponds to t 2 . x = quality of steam. 

item t 

The thermal efficiency as a boiler feed apparatus = 100 X . ■ . 

itemu 

item q + item s 

The thermal efficiency as a pump = 100 X : — • 

item u 

rp, , Ww (h + h 2 ) + w s h 2 ^ 

1 he horse power = (135) 

P 60 X 33,000 V *° 

The dry steam per horse power per hour = w 8 ' -J- item x. 

m , 1,000,000 + item p 

The pump duty = : 

item t 

1,000,000 [w w (h + h 2 ) + w 8 h 2 ] 



778w s (xr 3 +q a - q2 ) " " (I3 

The weight of steam found by direct weighing may be checked, by 

calculating (assuming radiation loss negligible) a " heat balance " in 
which this weight will be the only unknown, thus for this condition, 

i r v 2 ~\ 

w s (xr s +q s -q 2 ) = ==g \w w (h 1 +h 2 )+w.h2+(w w + w,) ^-\ +w w (q 2 - qi), 
or, approximately, 

wjh 1 + h 2 + 778 ( ff , - ffl ) + ~ 1 

778 (xr 3 + q a -q 2 )-h 2 ' ' ' ' ^ 37; 



CHAPTER XXIII 
TESTING THE STRENGTH OF MATERIALS 

Machines for Testing the Strength of Materials consist, in general, 
of (1) a power system for producing in the specimen tested the required 
stresses, and (2) a weighing system to determine the amount- of force 
applied. In the usual form of testing machine the load is applied to the 
specimen through a train of gears and screws operated either by power 
or by hand, depending, of course, largely on the capacity. The stress 
is measured by balancing the force exerted on the specimen by a poise 
adjusted at the end of a system of levers just as weight is determined with 
a platform scales. The general principle of most machines for testing 
materials is illustrated in a simple form in the apparatus for calibrating 
indicator springs, Fig. 120, page 116. In this case the power is applied 
to the hand wheel, which exerts two forces equal but opposite in direc- 
tion, one compressing the spring in the indicator and the other pressing 
on the platform of the scales. 

A diagrammatic view of a typical machine for testing materials in 
tension and compression is shown in Fig. 370. It consists essentially of 
a table T, to which the upper " head " A is rigidly attached by means of 
the vertical bars DD. Heavy vertical screws SS, carrying the lower 
cross-head B, are moved up or down by the system of gears GG. Moving 
the cross-head B downward puts a tensile stress on a test specimen s if 
it is attached firmly to both the upper " head " A and to the cross-head 
B. The force applied to the specimen is transmitted by the bars DD to 
the weighing table T, which rests on the first weighing lever M, having 
a fulcrum at F. The load on the table T is applied to the lever M at the 
middle of the table. The long arm of. this lever is connected by means 
of a short link to a second lever N, and this again is connected to the 
short arm of the lever Q at the other end of which the weighing poise P 
is to be balanced. The position of the poise on this last lever (scale 
beam) indicates the force applied to the specimen s. 

Fig. 371 is a remarkably good illustration for showing the parts of a 
standard testing machine and for explaining its operation. Vertical 
screws SS, connected by gearing to the power system, move the cross- 
head B up or down according to the direction of motion. The speed of 
these screws is controlled and their motion reversed by manipulation 
of the levers marked li, 1 2 , and 1 3 . The vertical columns supporting the 
upper " head " A are bolted to the table T, which rests on the system 

431 



432 



POWER PLANT TESTING 




Fig. 370. — Diagram of a Simple Machine for Testing the Strength of Materials. 




Fig. 371. — Standard Testing Machine. 



TESTING THE STRENGTH OF MATERIALS 433 

of levers M, N, and Q. The poise P is moved on the lever or scale- 
beam Q by means of a cord connected to the hand wheel W. The levers 
are balanced " to zero " by means of the counterpoise C. To prevent 
the sudden jarring of the machine when the load is released by the 
breaking of a specimen, vertical rods fastened to the base pass up 
loosely through holes in the table T, at its four corners, and on their 
ends large " check-nuts " are screwed. When the machine is in use 
these nuts must be loose, otherwise they will cause a pressure on the 
table causing the indication of the scale-beam to be greater than the 
weight due to the load on the specimen. 

Small testing machines with a capacity not exceeding 50,000 pounds 
are made to operate by hydraulic pressure. In this type of machine 
the movable head applying the load to the specimen is moved by the 
pressure on a piston in a hydraulic cylinder. This hydraulic pressure 
is produced usually in a small hand-operated pump at the side of the 
machine. Oil is generally used for the working medium. In order 
to return the oil to the pump from the cylinder, when the pressure is to 
be released, a small check valve controlled by a lever or a screw is usually 
provided. Machines operating hydraulically are not satisfactory for 
large loads, because the leakage from the cylinder is likely to be ex- 
cessive. 

When a specimen is to be tested in tension its upper end is fastened 
into the wedges or " jaws " in the upper " head " and its lower end 
is similarly gripped in the lower or movable cross-head. For tests in 
compression the specimen is placed between the movable cross-head 
and the table. Transverse loads can be applied to long wooden or 
metal beams with the machine shown in Fig. 371, by placing the beam 
between the supports or abutments UU', and applying the load by 
means of the movable cross-head B. Usually a special fitting with a blunt 
but " definable " edge to localize the load is inserted into the cross- 
head B for such tests. 

Extensometers. Some of the physical properties of materials are 
determined by the rate of deformation of the specimen as the stress is 
applied. To measure the deformation some very accurate instru- 
ments have been devised, one of which is shown in Fig. 372. It consists 
essentially of a pair of clamps CC, fitted with sharp-pointed thumb- 
screws for attaching them to the specimen SS. Two rods B and B', 
fitted to the upper clamp on opposite sides of the specimen, are pro- 
vided at their lower ends with adjustable points to be screwed up or 
down by means of the small milled wheels W and W. Opposite these 
rods and fastened to the lower clamp are two micrometer screws, usually 
graduated to ten-thousandths of an inch, for measuring the elongation 
of the specimen. Electrical connections are made, as shown, with a 



434 



POWER PLANT TESTING 



battery and a bell. As the specimen stretches out the contact points 
at P and P' are moved apart and the distance the micrometer screws 
are raised measures the elongation. With 
the help of the bell it is possible to make, 
for all observations, uniformly light con- 
tacts. 

Deflectometer. A very simple device for 
measuring the deflection of beams is shown 
in Fig. 373, consisting of a plate P sup- 
ported upon a steel bar attached to the end 
supports UU\ Deflections can be meas- 
ured with this apparatus with the aid of 
ordinary " inside " calipers, micrometer cal- 
ipers, or with a special deflectometer. This 
instrument illustrated in Fig. 374, is often 
used to measure the deflection of wooden 
and metal beams subjected to transverse 
stress. It can also be used with success to 
measure the contraction of short specimens 
in compression. 

Physical Properties of Materials Defined. 
The elastic limit is a more or less definite 
value of the unit stress beyond which, as 
the stress is increased, the increase in deformation is greater relatively 
than the increase in stress; and further, at this point, the deformations 
produced will not disappear entirely when the stress is removed. Per- 
manent set or "set" is used to represent the lasting deformations pro- 
duced by stresses greater than the elastic limit. 




Fig. 372. — Extensometer. 




3^? 



Fig. 373. — Simple Device for Measuring the Deflection of Beams. 



Modulus of Elasticity is a term used to express the ratio of the unit 
stress to the deformation per unit of length 1 accompanying that stress, 
within the elastic limit. For example, if f is the stress in pounds per 
square inch within the elastic limit and s is the accompanying defor- 

1 This unit deformation is often called the unit elongation for slender test-pieces, 
and more generally the strain. 



TESTING THE STRENGTH OF MATERIALS 



435 



mation per inch of length in inches, then the modulus of elasticity, 
in pounds per square inch, is 

E = f/s (140) 

The total stress under which a body fails is called its ultimate strength ; 
and the corresponding unit stress is called the ultimate unit strength, 
or, for short, simply the ultimate strength. The ratio of the total 
elongation of a body to its original length is called the percentage of 
elongation. It is obviously the same as the term unit deformation. 
For calculations of percentage of elongation measurements are taken, 
according to convention, between two gage marks usually 8 inches 
apart. This percentage of elongation is a measure of the ductility of 
the material tested. The ratio of the smallest area after rupture to the 
original area is called the " reduction of cross-section." 




Fig. 374. — Deflectometer. 

Resilience, often called the modulus of resilience, is a term used to 
represent the potential energy stored in a body; or, from another 
viewpoint, it is the amount of work that can be done by the body when 
relieved from a state of stress. More specifically, however, it is taken 
to mean in practice the work, in foot-pounds, done on a cubic inch of 
a material in stressing it to the elastic limit. For any value of the 
load the resilience is equal to the product of half the stress in pounds per 
square inch at the elastic limit times the distortion (usually the elonga- 
tion) of the test-piece in feet per inch of length up to the elastic limit, 
the latter term being the space passed through. Values of resilience 
calculated as thus defined may be checked by comparing with the 
square of the unit stress at the elastic limit divided by 24 times the 
value of the modulus of elasticity (E). 

Forms of Test-pieces for Tension Tests. Specimens for testing 
should be prepared with a great deal of care. Standard form for tests of 
flat bars 1 as well as for " coupons " cut from plates and structural shapes 
in tension is shown in Fig. 375. On such test-pieces marks one inch 
apart are usually made between the limits of the so-called gage length 

1 Adopted by American Society for Testing Material (1909). 



436 



POWER PLANT TESTING 



which is generally 8 inches. A standard scale similar to the one in 
Fig. 377 is of great assistance in marking a test-piece. At the left- 
hand end a percentage scale is shown from which the percentage of 



Parallel Section- 
not less than 9" 



"~ 



About VL^fiJtf' 
Radius 



LJ_L 



1 



■W-H 



W 



Lbijrat %'' 



Piece to be same thickness as plate 
Fig. 375. — Standard Flat Bar for Tension Tests. 

elongation, in a length of 8 inches, can be read directly. For testing 
round bars a shape shown in Fig. 376 is sometimes used, making the 
middle portion f inch in diameter. A special test piece of circular section 
only two inches long between the fillets where it is J inch in diameter 



Not less than 



1 to 3 

mad. 






Fig. 376. — Round Bar sometimes used for Tension Tests. 

is more generally recommended. The enlarged ends are f inch in diameter 
and have screw threads turned on them. 

Machine work on specimens for testing should be done carefully, so 
that the material is not torn or weakened in other ways. If there is 



40 S 

illinlimlim 



8 7 e 5 4 3 2 1 

jvi^jvr\jvj\jvr\J 



Fig. 377. — Scale for Marking Test-pieces. 

any flaw, marked irregularity or other defect in the material, the test- 
piece should be rejected. After a test-piece has been " necked " and 
broken as shown in Fig. 378, the accurate measurement of the elonga- 
tion is sometimes difficult. One method is to measure the elongation 



A 1 a 3 4 5 6 7 

Fig. 378. — Test-piece after Rupture. 



from the point of rupture toward each end. In materials in which the 
" necking " effect is very marked the measured amount of elongation 
will vary according to the distance of the fracture from the gage marks 



TESTING THE STRENGTH OF MATERIALS 437 

A and B. If the fracture is midway between these marks then nearly 
all the elongation will be between these marks ; but if the fracture is 
near one of the gage marks then a great deal of the elongation will fall 
outside of the marks, so that the measured elongation is too small. 
To correct for these discrepancies mentioned, a so-called " equivalent 
elongation " may be calculated by the following method: 

Assume that the standard test-piece, Fig. 375, has been divided 
originally into 8 equal spaces between the gage marks A and B, and that 
the nearest number of spaces between the points of fracture (Fig. 378) 
and the nearer gage mark is 3. The method may be stated that if the 
length between gage marks has been divided into x equal spaces and y 
is the nearest number of these spaces on the shorter portion between 
the point of rupture and the gage mark, then mark two points M and 
N on the longer portion, which are y and 1/2 x spaces, respectively, from 
the fracture. Place the two portions of the specimen as closely together 
as possible and measure from the gage mark in the short portion to the 
mark M. This distance, added to double the distance from M to N, 
gives the required total length after rupture. In this way the elongation 
of the " standard " length (x spaces) will be obtained, as if the fracture 
had occurred midway between the gage marks. To illustrate by the 
figure, there are 3 spaces on the shorter portion between the point of 
rupture and the gage mark B. The term y as defined above is therefore 
3. Then the total length to be compared with the original is to be 
measured on the broken test-piece from 2 to B, corresponding to 6 spaces, 
plus twice the distance from 1 to 2, corresponding to the remaining 2 
spaces to be accounted for. 

Specifications are often made to require that the fracture shall be 
within the " middle third of the length." 

Detailed Method for Tension Tests. A standard test-piece to be 
tested in tension should be without flaws or cracks, and furthermore the 
material should be monogeneous. Before putting it into the testing 
machine it should be carefully measured. With a scriber scratch the 
marks indicating one-inch divisions should be made with the " laying- 
off " gage. (Fig. 377.) Very light punch marks may then be made at 
each of the division marks accurately along the axis of the bar. 1 At each 
of these punch marks the diameter of the cross-section should be carefully 
measured with a micrometer caliper to thousandths of an inch. The 
outside punch marks, called the " gage marks," are often made a little 
heavier than the others, so that if an extensometer of the type illustrated 

1 Punch marks can be made accurately along the axis of a round bar by putting 
them at the "scratch" marks made with a scriber an inch apart along the length of 
the test-piece on the reflection of a "beam of light" on the bright surface of the test- 
piece. 



438 POWER PLANT TESTING 

in Fig. 372 is used, one of the thumbscrews supporting the clamps at each 
end can be set accurately but lightly into these marks. In this position 
the extensometer will measure accurately the elongation of the specimen 
between the gage marks. The testing machine to be used should then 
be balanced by adjusting the counterpoise provided for this purpose. 
It should be observed also that the " check-nuts " rest loosely on the 
table. As the load is increased, however, these nuts should be screwed 
down a little from time to time so that if the load is suddenly removed 
when the test-piece breaks, or should happen to slip out of the jaws or 
wedges holding it in place, the jar on the machine will be very much 
relieved. 

After balancing the machine the test-piece should be placed carefully 
and vertically between the " jaws " or wedges in both the upper and 
lower heads, and the extensometer should be put in position if one is to 
be used. Start the machine at a low rate of speed until a load of about 
1000 to 2000 pounds is indicated before taking any measurements of 
elongation. This first load is applied for the purpose of permitting the 
test-piece to assume a true central position, to allow for some slight 
slipping of the test-piece in the jaws before it becomes firmly gripped, 
and also to allow for possible irregularity in the adjustment of the extens- 
ometer or similar auxiliary apparatus. After this light load has been 
reached, during which time, doubtless for the kind of materials ordinarily 
tested, there will have been only a very small elongation, the load should 
be applied continuously and uniformly until the test-piece breaks, stop- 
ping only long enough, at the required intervals, to make the necessary 
observations of elongation and change of shape of the cross-section when 
" necking " begins. Increments of load are usually determined by taking 
one-tenth 1 the product obtained by multiplying the approximate esti- 
mated elastic limit of the material in pounds per square inch by the area 
of the cross-section in square inches. 

Near the elastic limit it is often found desirable to take observations 
at intervals of 500 pounds up to the yield point, where suddenly the rate 
of elongation increases very rapidly. By taking these observations at 
very close intervals at the elastic limit, data are secured which make the 
curves to be plotted much more satisfactory. 

In a standard test the stress, that is, the load, must never be decreased 
any appreciable amount when it is intended to apply still larger loads. 
A stress once applied must be maintained or increased continuously 
until the end of the test. Extensometers or other apparatus of delicate 
construction used for measuring the elongation should be removed 

1 In practice the increments of load in commercial tests are often one-half or one- 
third of the load at the elastic limit. For laboratory investigations it is not unusual 
to make the increments as small as one-twentieth of this load. 



TESTING THE STRENGTH OF MATERIALS 439 

from the test-piece before the specimen is broken. It is customary 
to take off such apparatuses just after the elastic limit is reached, 
although, as a rule, they can be left in place relatively longer for materials 
that are ductile than for those that are hard and brittle. Micrometers 
used on extensometers provided with electrical connections are to be set 
for readings on one side at a time, advancing the screw device until the 
bell rings, indicating that the contact has been made. Then turn it back 
just enough to stop the ringing of the bell, and advance the screw on the 
other side until the bell rings again. After also turning back the microm- 
eter screws just enough to stop the ringing, observations should be 
taken on both micrometers. Considerable time can be saved if, while 
these observations are being taken, the attendant having charge of the 
machine is meanwhile slowly advancing the load. The scale beam 
should be kept " floating " at all times during a test. Never run the 
balancing poise out on the scale beam beyond the point necessary to 
balance the beam. If the scale beam is carefully kept " floating " a 
point will be observed at from 50 to 75 per cent of the maximum load where 
the scale beam will fall, indicating apparently that it has been advanced 
too far. This point is called the yield point. It is defined as the stress 
at which the rate of elongation suddenly and rapidly increases. 

Beyond the elastic limit, when the extensometer has been removed, 
the rate of elongation can be measured with considerable accuracy by 
means of a large machinist's dividers, with the points set accurately on 
the " gage marks " at the ends of the standard length. 

The load when rupture occurs is not usually the maximum. When, 
therefore, considerable "necking" effect is observed, the poise on the. 
scale beam should be watched closely and when the maximum load has 
been reached, indicated by the falling of the scale beam, this weight 
should be quickly observed and recorded and then the poise should be 
brought back to follow the decreasing load. It will be observed that this 
part of the work is very interesting if it is done carefully. 

After the test-piece has been broken, stop the machine, remove the 
test-piece, clean and return the jaws or wedges to their proper places, 
and leave the machine in good order. 

The broken ends of the test-piece should be joined carefully and the 
length between each of the marks which were originally one inch apart 
should be measured. Check the sum of these lengths with the over-all 
length between the gage marks. With a micrometer, or preferably a 
vernier caliper, measure as accurately as possible the diameter of the 
smallest area at the fracture. The fracture should be carefully exam- 
ined to observe whether it is fibrous, granular or crystalline; whether 
coarse, fine or " silky;" whether cup-shaped, half-cup, or irregular in 
shape. 



440 POWER PLANT TESTING 

Curves and Calculations. Plot a curve with elongation per inch of 
length (" strain ") as abscissas and stress in pounds per square inch as 
ordinates. This is the familiar " stress-strain " diagram. 

Determine from the data obtained the modulus of elasticity (E), 1 the 
elastic limit, the maximum stress, the ultimate stress, per cent elongation 
in 8 inches, percentage elongation in 2 inches at the fracture, and per- 
centage reduction in area at the fracture. 

Plot a curve of elongation per inch, using for abscissas 2 the original 
length in inches and for ordinates the elongations measured for each inch 
between the gage marks. 

Report op Tension Tests 

1. Date and names of observers 

2. Material to be tested — specification 

3. Makers and brand of material 

4. Length between principal punch marks, before test 

5. Length between principal punch marks, after test 

6. Average width of test-piece, before test (6 readings) 

7. Average width of test-piece, after test (6 readings) 

8. Average thickness of test-piece, before test (9 readings) 

9. Average thickness of test-piece after test (6 readings) 

Readings to be taken, for observations 10 and 11 for increments of 2000 lbs. on 

scale beam until an elongation of 0.40 in. is obtained between readings and 
then by increments of 1000 lbs. until elongation of 0.03 in. is obtained between 
readings, and finally by 500 lbs. until piece nears point of maximum strength, 
when readings should be taken as frequently as possible, keeping beam balanced 
all the time. 

10. Total pull in pounds as shown by the machine 

11. Corresponding total elongation in piece in inches 

12. Yield point, pounds total (elastic limit) 

13. Maximum load, pounds total 

14. Breaking load, pounds total • 

15. Character of fracture, description and sketch 

The following results are to be computed: 

16. Original cross-section, sq. in 

17. Final cross-section, sq. in 

18. Reduction in area in sq. in., and in per cent of original area 

19. Final elongation, total and per cent 

20. Stress (pounds per square inch of original area) at elastic limit, maximum load 

and breaking load. 

y_ J The modulus of elasticity can be determined also from the " stress-strain " dia- 
gram by calculating the value of the tangent for the angle between a line drawn through 
the origin parallel to the straight part of " stress-strain " curve, reading the scales of 
coordinates, of course, in the units of stress and elongation marked on the diagram. 
It is obvious that the value of the tangent of the angle in this case is the unit stress 
divided by the unit elongation, which is, by definition, the modulus of elasticity. 

2 If on the curve sheet the " inch marks" on the test-piece are indicated by equal 
divisions on the scale of abscissas, then the points showing elongation for each inch 
should be plotted midway between the division lines indicating the position of the 
" inch marks." 



TESTING THE STRENGTH OF MATERIALS 441 

Tests in Compression. When a specimen of which the length is less 
than five times the smallest dimension is subjected to a load producing 
compression, it fails usually by crushing. Longer specimens fail usually 
by bending toward the side of least resistance. Two general classes of 
materials are frequently tested in compression: (1) Brittle materials, like 
brick, stone, wood, cement, cast iron, etc., which fail usually by shearing, 
and (2) plastic materials, like soft steel, wrought iron, copper, etc., which 
fail usually by a " flowing " of the metal. Because of the difficulty in 
measuring the deformations of short specimens of the plastic materials, 
and because the elastic limit in tension is invariably practically the same 
as in compression, these plastic materials are not often subjected to 
compressive loads. Methods to be explained here apply, therefore, par- 
ticularly to materials like wood, brick, stone, and cast iron. 

Detailed Method for Compression Tests of Short Test-pieces. Speci- 
mens of stone, cement, wood, or brick, of which the length is less than five 
times the smallest dimension, are usually provided in forms approximately 
cubes, although brick and wood are as often tested in the form of parallelo- 
pipeds similar to ordinary commercial bricks. Bearing surfaces, of 
specimens of stone, brick and cement should be made as nearly flat and 
parallel as possible, and should then be covered with a thin layer of plaster 
of Paris. Sized paper in thin sheets should be placed on the bearing 
surfaces between the specimen and the plaster to prevent the absorption 
of water from the latter. In order to have the plaster set in a true surface 
the specimen is placed between the " heads " of the testing machine for 
about ten minutes after the movable cross-head (B, Fig. 371) has been 
lowered to press lightly on the plaster. For tests in compression the 
test-piece is placed on the table T and the load is applied by lowering the 
movable cross-head B. 

Dimensions of test-pieces must be carefully measured and recorded 
before they are put into the testing machine; and, if any of them require 
the' application of plaster of Paris, then the measurements must be made 
before the plaster is put on. After balancing the testing machine by 
means of the counterweight with the test-piece on the table, apply the 
load continuously until the specimen is fractured; or in the case of plastic 
materials until the deformation is quite noticeable. In general conduct 
the test in the same way as for tension, 1 except that the specimen is 

1 Measurements of the amount of compression (shortening) of the test-piece can- 
not be made directly, but must be made between points on the heads of the testing 
machine. If there is likely to be much yielding of the parts of the machine, the mov- 
ing head should be lowered until its steel "compression plate" presses on the correspond- 
ing steel block on the table or lower platform with a force of about 1000 pounds. Now 
measure with micrometers the distance between the points on the two heads used for 
compression measurements, first with the load of 1000 pounds and then with additional 
increments of 1000 pounds up to considerably above the breaking load of the material 



442 POWER PLANT TESTING 

compressed instead of being stretched. If the material tested is cast 
iron or even hard stone or brick, precautions must be taken to protect 
persons near the machine from flying fragments. If the specimen begins 
to spall or flake off before it breaks down, the load corresponding as well 
as similar information should be recorded and placed in the tabulated 
report under " Remarks." Usually the specimen breaks down suddenly 
and the interior cone or pyramid in stone, brick, cement and cast iron 
will be plainly seen if the load has been " fairly " applied. In the case 
of tests of wood, this phenomenon will not be observed, but the lines of 
cleavage will usually show clearly a constant angle of shearing. 

Detailed Method of Compression Tests of Long Pieces (Columns). 
When the length of a specimen to be tested in compression is greater 
than, at the most, ten times its least dimension, it fails invariably by 
bending toward the side of least resistance. The condition of the ends 
of such test-pieces should be as nearly as possible either fixed or per- 
fectly free to turn. Either condition is, however, difficult to obtain. 
For test-pieces from 15 to 20 inches long usually an extensometer may be 
connected up to read the compression or shortening of the test-piece, if 
it is desired. 1 The observations will be taken in the same general way 
as for tension tests except that now the micrometer screws on the exten- 
someter will approach each other, so that these screws must be turned back 
after taking a measurement by an amount greater than the compression 
that will be produced by the next increment of load. 

Report on Compression Tests 

1. Date and names of observers 

2. Kind of material 

3. Average thickness of test-piece (4 readings), inches 

4. Average width of test-piece (4 readings), inches 

The machine is to be started and kept running continuously until fracture takes place, 
the beam being kept balanced carefully all the time. Readings are to be taken, and 
calculations made therefrom as follows: In making these tests wood and brick will 
be used and two pieces of each kind are to be tested, with each kind of stress. 

to be tested. From these data a correction curve should be plotted with which to cor- 
rect the deflections observed when the specimen is tested. 

When blocks of wood are to be tested in compression, readings of the micrometers 
should not be taken until a pressure of from 500 to 1000 pounds per square inch has 
been applied. This load will be required to crush the rough fibers. 

1 The lateral deflection along the neutral plane is sometimes determined by stretch- 
ing a fine wire along the length of the specimen parallel to the neutral axis. 



TESTING THE STRENGTH OF MATERIALS 



443 





















White Pine. 


Yellow Pine. 










1 


2 


1 


2 


* 


2 






Scale reading in pounds at time of fracture. 














Cross-section from items 3 and 4, square 




Breaking stress lbs. per square inch for 




Average breaking stress for each kind of 




Modulus of elasticity, lbs. per square inch. . . 





Sketches, Curves and Calculations. Sketch the character of the 
fracture for each specimen tested, indicating, for wood, the direction of 




Fig. 379. — Machine for Transverse Tests. 

the grain. Previously, the original shape of the specimen should have 
been sketched and dimensioned, 



444 POWER PLANT TESTING 

Calculate the maximum unit stress. 

If the material was suitable for the measurement of compression, plot 
" stress-strain " diagrams, and calculate the modulus of elasticity. 

Transverse Bending Tests. The most .common test by transverse or 
cross-bending is that of a beam usually of either wood or steel, of which 
the coefficient of elasticity and the " elastic curve " are desired. Deflec- 
tions of such beams give the data needed. Such tests may be made with 
a testing machine like the one shown in Fig. 371, which is provided with 
supporting abutments marked in the figure UU', and by inserting into 
the movable head the attachment for applying the load along a line across 
the beam rather than on a comparatively large area as in the tests already 
described when the load was applied directly by the flat surface of the 
cross-head B. Special transverse testing machines are, however, some- 
times available. A machine of this kind is illustrated in Fig. 379. 

In the Case of a wooden beam to be tested by loading at the middle, 
a fine steel wire should be stretched between two pins located as accu- 
rately as possible above the points of support and on the line of inter- 
section of the neutral plane with the side of the beam. The wire should 
be fastened to one of these pins and allowed to hang over the other, 
being kept taut by means of a weight attached to the free end, Fig. 380. 





-- 






- 














u 






I] 


u 





Fig. 380. — Device for Measuring the Deflection of a Wooden Beam. 

A steel scale, preferably highly polished so that it will show the image 
of the wire, should be attached in any suitable way to the side of the 
beam, so that the edge along which the scale readings to be observed 
are marked will be exactly half-way between the two supports. The 
beam must be protected from indentation by the knife-edges by small 
bearing plates. The load should be applied centrally in increments to 
give approximately 5^ inch deflections to the elastic limit, and beyond 
to give deflections of approximately ^ inch If it can be done succes- 
sively, the deflections should be read without stopping the test; unless, 
of course, the permanent set is to be determined, when after each incre- 
ment, the beam must be released from its load. 

Curves and Calculations. Plot a curve taking the load applied in 
pounds for abscissas and deflections in inches for ordinates. 

Sketch the character of the fracture. 



TESTING THE STRENGTH OF MATERIALS 445 

Calculate the modulus of elasticity, 1 the modulus of rupture, and 
the stress in the outer fiber at the elastic limit from the curve. 

Torsion Tests are made to determine the strength of a material to 
resist twisting forces. A typical machine for such tests is illustrated 
in Fig. 381. It consists in its essential parts of the frame FF', the 
" jaw " heads A and B for gripping the rod R to be tested, and the system 
of weighing levers on which the poise P is balanced. The load is applied 
to the rod R by power through the gears shown connected to the head B. 




Fig. 381. — Torsion Testing Machine. 

The power is applied by means of the pulley and gears shown at the 
right-hand side, or may be applied by hand power by turning hand 
wheels. With hand power usually more satisfactory results can be 
obtained than with power applied mechanically, because the rate of 
twisting can be more closely regulated. The amount of twist or the 

1 The modulus of elasticity is calculated by the formula 

E=^ (-4-) 

48 dl 



The modulus of rupture from 



. w M lc 

U = — - , (142) 

4 1 



and the stress in the outer fiber at the elastic limit by 



w e lc . . 

fe=— ~, (143) 

4 1 



when w e = load at the elastic limit in pounds per square inch; 

w u = load at the point of rupture in pounds per square inch; 
1 = length of beam (span) in inches; 
d = deflection in inches; 

c = distance from the neutral axis to the outer fiber in inches; 
I = moment of inertia, inch (4th power) units. 



446 POWER PLANT TESTING 

angular deformation is indicated by index-arms connected to opposite 
ends of the test-piece. 

1 An autographic torsion testing machine operated by hand power 
by means of the crank is sometimes used. The movement of the crank 
tends to rotate the test-piece which at the opposite end of the machine is 
fastened to a pendulum carrying a heavy bob. The resistance of the 
pendulum and its weight measure the power applied, which is equal to 
the length of the lever arm times the sine of the angle of inclination 
times the constant weight of the bob. 

Tests are made usually by increasing the twisting moment by incre- 
ments of about 200 inch-pounds, 1 measuring for each increment the 
torsion angle. 

Curves and Calculations. Plot a curve, using torsion angle for abscissas 
and twisting moment for ordinates. Calculate from this curve the unit 
stresses 2 (shearing) at the elastic limit, at the point of rupture, and 
also the maximum value of stress. Determine the torsion angle at 
the elastic limit and at the point of rupture, the helix angles, 3 and 
the modulus of elasticity for torsion. 4 

Impact Tests. Materials are tested by impact, usually by striking a 
test-piece with a weight allowed to fall upon it. Metals used in the 
manufacture of machinery and in railroad construction where it is 
likely to be subjected to shocks and blows are in many cases tested to 
determine the effect of the impact due to a blow. 

Some testing machines for such tests are made like a pile-driver with 

1 If tests are made of large sections of high-grade material, like, for example, a shaft 
of nickel steel for a students' class, it is expensive to break many specimens, so that 
for this reason the twisting moment producing a maximum stress just inside the elastic 
limit is computed before making the test, and this value is not to be exceeded. 

2 The unit stress is calculated with the formula: 

M/f, = V c, or f s = Mc/I p , (144) 

where M is the torsional moment in inch-pounds, c is distance in inches from the neutral 
axis to the extreme fiber, and I p is the polar moment of inertia. When c = r (the 
radius) as in the case of a cylindrical test-piece, I p = \ xt 4 . 

3 Torsion produces a peculiar arrangement of the outer fibers in the form of helices, 
as observed in broken test-pieces. Each one of these fibers makes an angle with its 
original position equal to its angular distortion a. Any particle on the surface is also 
moved through an angle /?, having its vertex in the axis and in a plane perpendicular 
to the axis. Now if we neglect the functions of small angles, we can write approxi- 
mately la = r/3, where 1 is the effective length of the test-piece and r is the radius. 
The helix-angle a = r/3/1. 

4 The modulus of elasticity in torsion (" modulus of rigidity "), 

E a = f s 4- a, 
as above, then 

E « = ^ (I45) 



TESTING THE STRENGTH OF MATERIALS 447 

the weight dropping vertically from a sort of gallows upon the test- 
piece. A more common form, however, of such machines consists 
of a pendulum provided with a heavy bob intended for delivering a blow 
on the middle of a test-piece in the shape of a bar, preferably" of a rect- 
angular section, held on two knife-edge supports attached to a heavy 
bedplate. Such machines are particularly designed for comparative 
tests of cast iron. They are provided with an arc concentric with the 
movement of the bob of the pendulum, graduated to read the verti- 
cal fall of the bob in feet. A tripping device is attached to the side 
of the graduated arc for permitting the bob to be supported and then 
dropped from any height within the limits of the machine. Since the 
deflection is very small, a device is usually supplied for magnifying it, 
and by means of a pencil-point traveling over a chart an autographic 
record is made of the deflections for each blow delivered by the bob. 
With such instruments the rebound of the test-piece and its permanent 
set must be carefully excluded from the measured deflection. One way 
to do this is to draw a " zero line " with the test-piece in place but before 
a blow is struck. Deflections and permanent set will then be measured 
on one side of this line and " rebounds " on the other. 

To determine the center load to be applied that will be equivalent 
to the impact, the following symbols are used : 
Let Wi = weight of the bob in pounds; 

h = the vertical distance it falls, in feet; 

W2 = the equivalent maximum center load, in pounds and 

d = the deflection in feet, then 

w x h = \ w 2 d, 

2Wih . ,. 

w 2 =— ^— (146) 

With this valve of w 2 the usual properties of the material may be calcu- 
lated by formulas (141), (142) and (143), page 445. 

Cement Tests. Cements are tested usually for (1) fineness; (2) time 
required for " setting " ; (3) tensile strength; (4) specific gravity; (5) sound- 
ness or freedom from cracks after setting; (6) crushing strength; and (7) 
toughness or ability to resist blows. Tests for crushing strength (com- 
pression) are usually made by crushing cubical blocks in a testing 
machine designed for general tension and compression tests (see page 
432). For tensile tests, however, special machines, designed particularly 
for testing cement, are generally used. Because of the nature of the 
material it is absolutely necessary that the power be applied in the line 
of the axis of the test-piece and also with steadiness and in increments 
as uniform as possible. There is a standard size and shape for test- 
pieces of cement, and they must be made in a certain prescribed way 



448 



POWER PLANT TESTING 




Fig. 



385. — Standard Cement 
Briquette. 



in order that different tests may be compared. The standard briquette 
for testing (one square inch section) is shown in Fig. 385. The strength 
of the briquettes is affected by the time allowed for hardening, the amount 

of water used, and by the method of mix- 
ing the cement. 

Power is applied in the automatic 
cement-testing machine in Fig. 387, by 
shot dropped from a cylindrical hopper 
into a pail supported on a scales. The 
briquette of cement being tested is held 
between two shackles or "holders" con- 
nected to a hand wheel used to regulate 
the distance between the shackles. When 
a briquette breaks the scale beam drops, 
and closes automatically a valve, stop- 
ping the delivery of shot into the pail. 
The operation of the machine may be 
described briefly as follows: Hang the 
hopper on the hook as shown and put 
enough shot into it to balance the coun- 
terpoise. Now put the briquette into the 
shackles and adjust the hand wheel so that the scale beam will rise nearly 
to the stop. When the valve is opened shot will begin to fall into the pail. 
The delivery of the shot into the pail should be slow. When the briquette 
has broken, the scale beam has dropped and the valve has been closed. 
The weight of shot collected in the pail shows the number of pounds 
required to break the briquette. 

A non-automatic type of cement-testing machine is illustrated in 
Fig. 388. In this machine the power is applied by moving a hand wheel 
operating by means of a screw the system of levers transmitting the load 
to the briquette in the shackles. The tension produced by this load may 
obviously be balanced by weights applied to the scale beam above. In 
order to secure a very uniform and slow movement of the poise it is 
carried along the scale beam by a cord moved by a small crank. In 
applying the load the hand wheel should be moved as slowly and uni- 
formly as possible to avoid a jerking motion. In the figure one of the 
standard briquette moulds, and a tray used for immersing the briquettes 
in water after they have set are shown. Fig. 389 shows the proper 
position of the briquette in the supporting shackles. 

Test of Cement for Fineness is made by determining the amount by 
weight of a given sample that will not pass through sieves with meshes 
of a standard size. The American Society of Civil Engineers recommends 
the use of sieves of 2500, 5476 and 10,000 meshes per square inch. Sieves 



TESTING THE STRENGTH OF MATERIALS 



449 



with approximately these meshings are known as Nos. 50, 80, and 100; 
that is, they have this number of meshes to the linear inch. A weighed 
sample of cement is first passed through a No. 50 sieve and the weight of 
that remaining in the sieve is recorded. That passing through is then 
put into the next sieve (No. 80) and the residue in this sieve is likewise 
weighed, while that passing through goes to the finest sieve (No. 100). 




Fig. 387. — Automatic Cement Testing Machine. 



Results of this test for fineness are expressed by the percentages that the 
various residues remaining in the sieves are of the original weight of the 
sample. 

Unless cement is ground as fine as flour it has very little " binding 
power." The coarse particles are nearly as inert for " cementing " as 
sand. 

Throughout America generally the following methods for testing 
cement adopted by the American Society of Civil Engineers in 1903 and 
1904 and revised in January, 1909, are used; 



450 



POWER PLANT TESTING 



Selection of Sample. The selection of the sample for testing is a detail 
that must be left to the discretion of the engineer ; the number and the 
quantity to be taken from each package will depend largely on the 
importance of the work, the number of tests to be made and the facilities 
for making them. 




Fig. 388. — Hand-operated Cement Testing Machine. 



The sample shall be a fair average of the contents of the package ; it is 
recommended that, where conditions permit, one barrel in every ten be 
sampled. 

Samples should be passed through a sieve having twenty meshes per 
linear inch, in order to break up lumps and remove foreign material; 
this is also a very effective method for mixing them together in order 
to obtain an average. 

Method of Sampling. Cement in barrels should be sampled through 
a hole made in the center of one of the staves, midway between the heads, 



TESTING THE STRENGTH OF MATERIALS 



451 



or in the head, by means of an auger or a sampling iron similar to that 
used by sugar inspectors. If in bags, it should be taken from surface to 
center. 

Chemical Analysis. As a method to be followed for the analysis of 
cement, that proposed by the Committee on Uniformity in the Analysis 
of Materials for the Portland Cement Industry, of the New York Section 
of the Society for Chemical Industry, and published in Engineering News, 
Vol. 50, p. 60, 1903, is recommended. 

Specific Gravity. The specific gravity of cement is lowered by adult- 
eration and hydration; but the adulteration must be in considerable 
quantity to affect the results appreciably. Inasmuch as the differences 
in specific gravity are usually very small, great care must be exercised in 
making the determination. 

The determination of specific gravity is most conveniently made with 
Le Chatelier's apparatus. This consists of a flask (D), Fig. 390, of 120 
cu. cm. (7.32 cu. in.) capacity, the neck of which is about 20 cm. 



bW 





Fig. 389. — Briquette in 
Shackles. 



Fig. 390. — Le Chatelier'i 
Specific Gravity Flask. 



(7.87 in.) long; in the middle of this neck is a bulb (C), above and below 
which are two marks (F) and (E); the volume between these marks is 
20 cu. cm. (1.22 cu. in.) The neck has a diameter of about 9 mm. 
(0.35 in.), and is graduated into tenths of cubic centimeters above the 
mark (F). Benzine (62° Baume naphtha), or kerosene free from water, 
should be used in making the determination. Specific gravity can 
be determined in two ways : 

(1) The flask is filled with either of these liquids to the lower mark 
(E), and 64 grams (2.25 oz.) of powder, cooled to the temperature of the 
liquid, is gradually introduced through the funnel (B) [the stem of which 
extends into the flask to the top of the bulb (C)], until the upper mark 



452 POWER PLANT TESTING 

(F) is reached. The difference in weight between the cement remaining 
and the original quantity (64 g.) is the weight which has displaced 
20 cu. cm. 

(2) The whole quantity of the powder is introduced, and the level 
of the liquid rises to some division of the graduated neck. This reading 
plus 20 cu. cm. is the volume displaced by 64 g. of the powder. The 
specific gravity is then obtained from the formula: 

q -f, n •+ _ Weight of Cement, in grams 

Displaced Volume, in cubic centimeters 

The flask during the operation is kept immersed in water in a jar 
(A), in order to avoid variations in the temperature of the liquid. The 
results should agree within 0.01. The determination of specific gravity 
should be made on the cement as received;, and, should it fall below 
3.10, a second determination should be made on the sample ignited at 
a low red heat. 

A convenient method for cleaning the apparatus is as follows: The 
flask is inverted over a large vessel, preferably a glass jar, and shaken 
vertically until the liquid starts to flow freely; it is then held still in a ver- 
tical position until empty; the remaining traces of cement can be re- 
moved in a similar manner by pouring into the flask a small quantity 
of clean liquid and repeating the operation. 

Fineness. It is generally accepted that the coarser particles in cement 
are practically inert, and it is only the extremely fine powder that possesses 
adhesive or cementing qualities. The more finely cement is pulverized, 
all other conditions being the same, the more sand it will carry and 
produce a mortar of a given strength. The degree of final pulverization 
which the cement receives at the place of manufacture is ascertained by 
measuring the residue retained on certain sieves. Those known as the 
No. 100 and No. 200 sieves are recommended for this purpose. 

The sieves should be circular, about 20 cm. (7.87 in.) in diameter, 6 cm. 
(2.36 in.) high, and provided with a pan 5 cm. (1.97 in.) deep, and a 
cover. The wire cloth should be of brass wire having the following 
diameters: No. 100, 0.0045 in.; No. 200, 0.0024 in. This cloth should 
be mounted on the frames without distortion; the mesh should be 
regular in spacing and be within the following limits: No. 100, 96 to 
100 meshes to the linear inch; No. 200, 188 to 200 meshes to the linear 
inch. 

Fifty grams (1.76 oz.) or 100 grams (3.52 oz.) should be used for the test, 
and dried at a temperature of 100 deg. Cent. (212 deg. Fahr.) prior to 
sieving. The thoroughly dried and coarsely screened sample is weighed 
and placed on the No. 200 sieve, which, with pan and cover attached, 
is held in one hand in a slightly inclined position, and moved forward 



TESTING THE STRENGTH OF MATERIALS 



453 



and backward, at the same time striking the side gently with the palm 
of the other hand, at the rate of about 200 strokes per minute. The 
operation is continued until not more than one-tenth of 1 per cent 
passes through after one minute of continuous sieving. The residue 
is weighed, then placed on the No. 100 sieve and the operation repeated. 
The work may be expedited by placing in the sieve a small quantity of 
steel shot. The results should be reported to the nearest tenth of 1 
per cent. 

Normal Consistency. The use of a proper percentage of water in 
making the pastes 1 from which pats, tests of setting, and briquettes 
are made, is exceedingly important, and affects vitally the results ob- 
tained. The determination consists in measuring the amount of water 
required to reduce the cement to a given state of plasticity, or to what 
is usually designated as the normal consistency. 

Method, Vicat Needle Apparatus. — This consists of a frame (K), Fig. 
391, bearing a movable rod (L), with the cap (A) at one end, and at 
the other a cylinder 1 cm. (0.39 in.) in diam- 
eter, the cap, rod and cylinder weighing 300 
grams (10.58 oz.). The rod, which can be 
held in any desired position by a screw (F) 
carries an indicator, which moves over a scale 
(graduated to centimeters) attached to the 
frame (K). The paste is held by a conical, 
hard-rubber ring (I), 7 cm. (2.76 in.) in diam- 
eter at the base, 4 cm. (1.57 in.) high, resting 
on a glass plate (J), about 10 cm. (3.94 in.) 
square. 

In making the determination the same quan- 
tity of cement as will be subsequently used 
for each batch in making the briquettes, but 
not less than 500 grams, is kneaded into a paste, 
as described, and quickly formed into a ball 
with the hands, completing the operation by 
tossing it six times from one hand to the 
other, maintained 6 inches apart; the ball is 
then pressed into the rubber ring, through the larger opening, smoothed off, 
and placed (on its large end) on a glass plate and the smaller end smoothed 
off with a trowel; the paste, confined in the ring, resting on the plate, is 
placed under the rod bearing the cylinder, which is brought in contact 
with the surface and quickly released. The paste is of normal consist- 
ency when the cylinder penetrates to a point in the mass 10 mm. (0.39 in.) 

1 The term " paste " is used in this report to designate a mixture of cement and 
water, and the word " mortar " a mixture of cement, sand and water. 




391. —Vicat Needle 
Apparatus. 



454 



POWER PLANT TESTING 



below the top of the ring. Great care must be taken to fill the ring 
exactly to the top. Trial pastes are made with varying percentages 
of water until the correct consistency is obtained. The Committee has 
recommended, as normal, a paste, the consistency of which is rather 
wet, because it believes that variations in the amount of compression 
to which the briquette is subjected in moulding are likely to be less with 
such a paste. Having determined in this manner the proper percentage 
of water required to produce a paste of normal consistency, the proper 
percentage required for the mortars is obtained from an empirical for- 
mula. The subject proves to be a very difficult one, and although the 
committee has given it much study, it is not yet prepared to make a 
definite recommendation. The Committee inserts the following table : 



PERCENTAGE OF WATER FOR STANDARD MIXTURES 



Neat 


1 to 1 


lto2 


1 to 3 


lto4 


1 to 5 


Neat 


1 tol 


lto 2 


lto 3 


lto 4 


1 to 5 


18 


12.0 


10.0 


9.0 


8.4 


8.0 


33 


17.0 


13.3 


11.5 


10.4 


9.6 


19 


12.3 


10.2 


9.2 


8.5 


8.1 


34 


17.3 


13.6 


11.7 


10.5 


9.7 


20 


• 12.7 


10.4 


9.3 


8.7 


8.2 


35 


17.7 


13.8 


11.8 


10.7 


9.9 


21 


13.0 


10.7 


9.5 


8.8 


8.3 


36 


18.0 


14.0 


12.0 


10.8 


10.0 


22 


13.3 


10.9 


9.7 


8.9 


8.4 


37 


18.3 


14.2 


12.2 


10.9 


10.1 


23 


13.7 


11.1 


9.8 


9.1 


8.5 


38 


18.7 


14.4 


12.3 


11.1 


10.2 


24 


14.0 


11.3 


10.0 


9.2 


8.6 


39 


19.0 


14.7 


12.5 


11. 2' 


10.3 


25 


14.3 


11.6 


10.2 


9.3 


8.8 


40 


19.3 


14.9 


12.7 


11.3 


10.4 


26 


14.7 


11.8 


10.3 


9.5 


8.9 


41 


19.7 


15.1 


12.8 


11.5 


10.5 


27 


15.0 


12.0 


10.5 


9.6 


9.0 


42 


20.0 


15.3 


13.0 


11.6 


10.6 


28 


15.3 


12.2 


10.7 


9.7 


9.1 


43 


20.3 


15.6 


13.2 


11.7 


10.7 


29 


15.7 


12.5 


10.8 


9.9 


9.2 


44 


20.7 


15.8 


13.3 


11.9 


10.8 


30 


16.0 


12.7 


11.0 


10.0 


9.3 


45 


21.0 


16.0 


13.5 


12.0 


11.0 


31 


16.3 


12.9 


11.2 


10.1 


9.4 


46 


21.3 


16.1 


13.7 


12.1 


11.1 


32 


16.7 


13.1 


11.3 


10.3 


9.5 
















lto 1 


lto 2 


lto 3 


lto 4 


lto 5 




t 










500 
500 


33 
66 


3 
3 




250 
750 


200 
800 






167 












833 















Time of Setting. The object of this test is to determine the time 
which elapses from the moment water is added until the paste ceases 
to be fluid and plastic (called the " initial set "), and also the time re- 
quired for it to acquire a certain degree of hardness (called the " final " 
or "hard set"). The former of these is the more important since, 
with the commencement of setting, the process of crystallization or 
hardening is said to begin. As a disturbance of this process may produce 
a loss of strength, it is desirable to complete the operation of mixing 
and moulding or incorporating the mortar into the work before the cement 
begins to set. It is usual to measure arbitrarily the beginning and end 



TESTING THE STRENGTH OF MATERIALS 455 

of the setting by the penetration of weighted wires of given diameters. 
For this purpose the Vicat Needle, Fig. 391, should be used. In making 
the test, a paste of normal consistency is moulded and placed under the 
rod (L), bearing the cap (A) at one end and the needle (H), 1 mm. (0.039 
in.) in diameter, at the other, weighing 300 grams (10.58 oz.). The 
needle is then carefully brought in contact with the surface of the paste 
and quickly released. 

The setting is said to have commenced when the needle ceases to 
pass a point 5 mm. (0.20 in.) above the upper surface of the glass plate, 
and is said to have terminated the moment the needle does not sink 
visibly into the mass. Test-pieces should be stored in moist air during 
the test; this is accomplished by placing them on a rack over water 
contained in a pan and covered with a damp cloth, the cloth to be kept 
away from them by means of a wire screen; or they may be stored in 
a moist box or closet. Care should be taken to keep the needle clean, 
as the collection of cement on the sides of the needle retards the penetra- 
tion, while cement on the point reduces the area and tends to increase 
the penetration. The determination of the time of setting is only approx- 
imate, being materially affected by the temperature of the mixing water, 
the temperature and humidity of the air during the test, the percentage 
of water used, and the amount of molding the paste receives. 

Standard Sand. The Committee recognizes the grave objections to 
the standard quartz now generally used, especially on account of its 
high percentage of voids, the difficulty of compacting in the moulds, 
and its lack of uniformity; it has spent much time in investigating 
the various natural sands which appeared to be available and suit- 
able for use. For the present, the Committee recommends the natural 
sand from Ottawa, 111., screened to pass a sieve having 20 meshes per 
linear inch and retained on a sieve having 30 meshes per linear inch; 
the wires to have diameters of 0.0165 and 0.0112 in., respectively, i.e., 
half the width of the opening in each case. Sand having passed the No. 
20 sieve shall be considered standard when not more than 1 per cent 
passes a No. 30 sieve after one minute's continuous sifting of a 500 g. 
sample. 1 

Form of Briquette. While the form of the briquette recommended 
by a former Committee of the Society is not wholly satisfactory, this 
Committee is not prepared to suggest any change, other than rounding 
off the corners by curves of |-in. radius, Fig. 383. 

Molds. The molds should be made of brass, bronze, or some equally 
non-corrodible material, having sufficient metal in the sides to prevent 

1 The Sandusky Portland Cement Company, of Sandusky, Ohio, has agreed to 
undertake the preparation of this sand, and to furnish it at a price only sufficient to 
cover the actual cost of preparation. 



456 POWER PLANT TESTING 

spreading during molding. Gang molds, which permit molding a 
number of briquettes at one time, are preferred by many to single molds, 
since the greater quantity of mortar that can be mixed tends to produce 
greater uniformity in the results. The type shown in Fig. 393 is recom- 
mended. The molds should be wiped with an oily cloth before using. 




J\ 



'/z^^j 



Fig. 393.— Briquette Mold. 

Mixing. All proportions should be stated by weight; the quantity 
of water to be used should be stated as a percentage of the dry material. 
The metric system is recommended because of the convenient relation 
of the gramme and the cubic centimeter. The temperature of the room 
and the mixing water should be as near 21 deg. Cent. (70 deg. Fahr.) as it is 
practicable to maintain it. The sand and cement should be thoroughly 
mixed dry. The mixing should be done on some non-absorbing surface, 
preferably plate glass. If the mixing must be done on an absorbing 
surface it should be thoroughly dampened prior to use. The quantity 
of material to be mixed at one time depends on the number of test pieces 
to be made; about 1000 grams (35.28 oz.) makes a convenient quantity 
to mix, especially by hand methods. The material is weighed and 
placed on the mixing table, and a crater formed in the center, into which 
the proper percentage of clean water is poured; the material on the 
outer edge is turned into the crater by the aid of a trowel. As soon 
as the water has been absorbed, which should not require more than 
one minute, the operation is completed by vigorously kneading with 
the hands for an additional one and a half minutes, the process being 
similar to that used in kneading dough. During the operation of mixing, 
the hands should be protected by gloves, preferably of rubber. 

Molding. Having worked the paste or the mortar consistency it is 
at once placed in the molds by hand. The molds should be rilled im- 
mediately after the mixing is completed, the material pressed in firmly 
with the fingers and smoothed off with a trowel without mechanical 
ramming; the material should, be heaped up on the upper surface of 
the mold, and, in smoothing off, the trowel should be drawn over the 
mold in such a manner as to exert a moderate pressure on the excess 
material. The mold should be turned over and the operation repeated. 

A check upon the uniformity of the mixing and molding is afforded 
by weighing the briquettes just prior to immersion, or upon removal 



TESTING THE STRENGTH OF MATERIALS 457 

from the moist closet. Briquettes which vary in weight more than 
3 per cent from the average should not be tested. 

Storage of Test-pieces. During the first twenty-four hours after 
molding, the test-pieces should be kept in moist air to prevent them 
from drying out. A moist closet or chamber is so easily devised that 
the use of the damp cloth should be abandoned if possible. Covering the 
test-pieces with a damp cloth is objectionable, as commonly used, be- 
cause the cloth may dry out unequally, and, in consequence, the test- 
pieces are not all maintained under the same condition. Where a moist 
closet is not available, a cloth may be used and kept uniformly wet by 
immersing the ends in water. It should be kept from direct contact 
with the test-pieces by means of a wire screen or some similar arrange- 
ment. A moist closet consists of a soapstone or slate box, or a metal- 
lined wooden box — the lining being covered with felt and this felt kept 
wet. The bottom of the box is so constructed as to hold water, and the 
sides are provided with cleats for holding glass shelves on which to 
place the briquettes. Care should be taken to keep the air in the closet 
uniformly moist. After twenty-four hours in moist air, the test-pieces 
for longer periods of time should be immersed in water maintained as 
near 21 deg. Cent. (70 deg. Fahr.) as practicable; they may be stored in 
tanks or pans, which should be of non-corrodible material. 

Tensile Strength. The tests may be made on any standard machine. 
A solid metal clip, as shown in Fig. 389 (page 451), is recommended. 
This clip is to be used without cushioning at the points of contact with 
the test specimen. The bearing at each point of contact should be 
J in. wide, and the distance between the center of contact on the same 
clip should be 1| in. Test pieces should be broken as soon as they are 
removed from the water. Care should be observed in centering the 
briquettes in the testing machine, as cross-strains, produced by improper 
centering, tend to lower the breaking strength. The load should not 
be applied too suddenly, as it may produce vibration, the shock from 
which often breaks the briquette before the ultimate strength is reached. 
Care must be taken that the clips and the sides of the briquette be clean 
and free from grains of sand or dirt, which would prevent a good bearing. 
The load should be applied at the rate of 600 lbs. per min. The average 
of the briquettes of each sample tested should be taken as the test, 
excluding any results which are manifestly faulty. 

Constancy of Volume. The object is to develop those qualities which 
tend to destroy the strength and durability of a cement. As it is highly 
essential to determine such qualities at once, tests of this character 
are for the most part made in a very short time, and are known, therefore, 
as accelerated tests. Failure is revealed by cracking, checking, swelling, 
or disintegration, or all of these phenomena. A cement which remains 



458 



POWER PLANT TESTING 



perfectly sound is said to be of constant volume. Tests for constancy 
of volume are divided into two classes: (JL) normal tests, or those made in 
either air or water maintained at about 21 deg. Cent. (70 deg. Fahr.), and (2) 
accelerated tests, or those made in air, steam, or water at a temperature 
of 45 deg. Cent. (115 deg. Fahr.) and upward. The test-pieces should be 
allowed to remain 24 hours in moist air before immersion in water or 
steam, or preservation in air. For these tests pats, about 7| cm. (2.95 in.) 
in diameter, 1| cm. (0.49 in.) thick at the center, and tapering to a thin 
edge, should be made upon a clean glass plate [about 10 cm. (3.94 in.; 
square], from cement paste of normal consistency. 

Normal Test. A pat is immersed in water maintained as near 21 deg. 
Cent. (70 deg. Fahr.) as possible for 28 days, and observed at intervals. 
A similar pat, after 24 hours in moist air, is maintained in air at ordinary 
temperature and observed at intervals. 

Data regarding tests of neat cement and mortar briquettes may be 
tabulated in a form similar to the following: 



FORM FOR CEMENT TESTS 



1. Date, and names of observers. 

2. Name and kind of cement. 

3. Makers and location of plant. 

4. Distinguishing mark on briquettes. 

5. Date of mixing and time. 

6. Temperature of room at time of mixing, deg. F. 

7. Temperature of water at time of mixing, deg. F. 

8. Conditions of setting: as to time briquettes were left iu dampened : 

9. Activity of the cement or time of initial and final setting. 1 
10. Fineness of grinding. 



before immersion, etc. 



Kind of Briquette. 



Composition 

of 
Briquettes. 



Per Cent of Cement . 
Per Cent of Water . . 



Per Cent of Cement. 
Per Cent of Water.. 
Per Cent of Sand.... 



No. of Briquettes. 



12 3 4 



Time of test. 
Breaking strength, lbs. 
Appearance of fracture 

— give sketch of each 

here. 
Temp, of room at time 

of test. deg. F. 



28 Day. 





7 Day. 






28 Day 




1 


2 


3 


4 


5 


• 


7 


S 



















In reporting the results of these experiments it is important that the effect of different percentages of water 
sand, etc., and time of immersion, be fully discussed. 



See pages 454 and 455. 



TESTING THE STRENGTH OF MATERIALS 459 

Accelerated Test. A pat is exposed in any convenient way in an at- 
mosphere of steam, above boiling water, in a loosely closed vessel, 1 
for 5 hours. To pass these tests satisfactorily, the pats should remain 
firm and hard, and show no signs of cracking, distortion or disintegration. 
Should the pat leave the plate, distortion may be detected best with 
a straight-edge applied to the surface which was in contact with the 
plate. 

1 The apparatus recommended for this test is shown with a dimensioned drawing 
in Proc. A.S.C.E., vol. 35, No. 2 (1909). 



CHAPTER XXIV 

OUTLINES OF SUGGESTED TESTS 

i. Calibration and Adjustment of Pressure Gage. Reference, pages 7-22. 

Apparatus. Dead weight gage tester, standard weights, and gage to be tested. 

Method. Take readings at intervals of 5 lbs. per sq. in., up and down. Spin platform 
and weights to eliminate friction. Remove the indicating needle with special jack and 
take off dial. Sketch parts in interior of gage. Reset needle to read correctly in part 
of scale most used. 1 Attach needle firmly. Repeat readings up and down for new 
calibration. 

Report. Explain methods of adjustment. Tabulate as on page 21. 

Curves. 2 (See page 22.) Draw curves only for final condition of gage. 

2. Calibration and Adjustment of Vacuum Gage. Reference, pages 22-24 and 236. 
Apparatus. Mercury U-tube, aspirator (ejector) or air pump, and gage to be tested. 
Method. Take readings at intervals of 2 in. vacuum, up and down. If there is water 

or other impurity on mercury column correction must be made. (Reset needle if so 
instructed.) 

Report. Explain details of method used. Tabulate as on page 21, omitting second 
column and writing " ins. vac. " for "pressure, lbs. per sq. in." 

Curves. Similar to instructions for test No. 1. 

3. Thermometer Calibration for Range Above 212 F. Reference, pages 29-39. 
Apparatus. Steam gage used in test No. 1, thermometers (a standard high-reading 

thermometer is sometimes used to check the results), barometer and steam tables 
(pages 468-470). 

Method. Read thermometer being tested (and " standard " if one is used) at intervals 
of approximately 5 lbs. per sq. in. on the gage calibrated in test No. 1. Be sure the 
steam is not superheated and allow at least 5 min. after final adjustments of valves before 
readings are taken. 

Report. Sketch with a simple line drawing the interior of apparatus used with neces- 
sary piping connections. Tabulate as on page 37. Calculate " stem " corrections when 
necessary. 

Curves. (See page 36.) " True " temperatures are from steam tables. 

4. Use and Calibration of a Planimeter. Reference, pages 74-87, 141. 
Apparatus. Polar planimeter, large compass, scale, and micrometer. 

Method. 1. Measure length of tracing-arm from pivot to tracing-point and diameter 
of rolling or graduated wheel to check accuracy for reading areas in sq. in. 
1 2. Calculate length of tracing-arm so that one revolution of graduated wheel will 
indicate 8 sq. in. 

3. Find area of zero circle by at least two methods (see pages 77, 80). 

4. Determine average error in per cent of instrument by first measuring and 
then calculating the area of circles of 1, 2, and 3 in. diameter (see page 87, footnote). 

1 If other instructions are not given assume two-thirds maximum graduation of dial. 

2 Arrangement of coordinates for curves is throughout to make them most applicable 
for use; that is, in the use of a curve the given quantity should be read on the scale of 
abscissas and the value to be found will then be obtained from the scale of ordinates. 

460 



OUTLINE OF SUGGESTED TESTS 461 

Measure each area three times and take average. Mark percentage error + if instru- 
ment reads too small and — if too large. 

5. Determine indicated horse power for an indicator card. Scale of indicator spring 
= 40 lbs. per sq. in. (i.e., No. 40 spring); area of piston •= 66 sq in.; length of stroke = 
lft.; andr.p.m. = 200. 

Report. Record data, method of measurements, and calculations. Tabulate results. 

5. Calibration of Indicator Springs in Compression. Reference, pages 92-106, 
112-120, 136-144. Read Precautions for Care of Indicator, pages 103-106. 

Apparatus. Indicator, set of springs, and indicator spring tester. 

Method. 1. Test perpendicularity of motion of pencil-point to atmospheric line. 
(Footnote, page 105.) 

2. Obtain at least two good calibration cards for each spring similar to Fig. 121, for 
increasing and decreasing pressures. Obviously unless the cards obtained for a spring 
are alike, the work is not successful. Take increments of 5 lbs. per sq. in. for all springs 
up to and including the " 40 lb." spring. For springs of higher scale take increments 
of 10 lbs. per sq. in. Lines of maximum pressure on calibration card should be about 
If ins. above the atmospheric line. 

When a plunger type of tester is used, that is, similar in principle to Fig. 118, the 
diameter of the plunger must be measured with a micrometer and the relation accurately 
calculated between the weight and the unit pressure applied to the indicator in lbs. per 
sq. in. 

Examine at least two types of indicators. Insert the spring and study the adjustment 
of the height of the pencil. 

When work with an indicator is finished, always remove the " piston " spring and 
thoroughly clean all parts, inside and outside. 

Report. Tabulate and draw curves as directed on page 119. Calculate the true 
scale of spring from the average of four equidistant points on this curve. Explain 
calculations. Discuss any discrepancies in data. 

If a " 40-lb." spring has been calibrated, assume this was used in obtaining the indi- 
cator card used in test No. 4, and calculate the corrected indicated horse power. 

5a. Calibration of Indicator Springs in Tension (for use with Vacuum). Reference, 
pages 118, 119. 

Apparatus. Indicator, springs, and special tester. 

Method and report same as for test No. 5. 

6. Study of Reducing Motions. Reference, pages 121-138. 
Apparatus. Steel scale and drawing instruments. 

Method and Report. Examine reducing motions in laboratory. Design an accurate 
device for an engine as designated by instructor. 

7. Calorimeter Tests, Use and Comparison. Reference, pages 55-73. 
Apparatus. Separating calorimeter, glass beaker (or graduate), pail with cover 

having a hole for insertion of hose for condensing steam, platform scales, watch, throt- 
tling calorimeter, thermometers, steam pressure gage, barometer and monkey wrench. 

Method. Calibrate steam gage,. Connect the separating and throttling calorimeters 
by means of standard sampling nipples (see page 56) to the same vertical steam pipe 
where they will both take steam of the same quality. Allow steam to blow through 
both calorimeters until the temperatures in the throttling type have reached a maximum 
value and the other has become thoroughly heated and enough water has collected to 
bring the level in the water gage glass up to, or a little above, the zero on the scale. 
Make the condensing pail about two-thirds full of water. Obtain this weight of water 
by weighings. When all conditions are satisfactory, put the hose through which steam 
has been discharging from the separating calorimeter into the hole in the cover of the 
pail, and at the same time observe reading of scale of water gage. Read temperatures 



462 POWER PLANT TESTING 

and pressures every three minutes. Run the test until an appreciable volume of steam 
discharges from the hole in the cover of the pail. Then throw steam tube out of pail 
and read the level in the water gage. Again weigh pail and contents. Calibrate the 
scale of the water gage by removing and weighing water from the separating calorimeter 
between any two levels within the limits of the scale. 

Make one test at each of four steam pressures above 60 lbs. per sq. in. gage as 
designated by instructor. 

Calculate the quality of steam roughly by the charts on pages 59 or 61 during the 
progress of the tests and immediately check with data from separating calorimeter. 

Report. Tabulate all observed and calculated data. Sketch and describe fully the 
calorimeters used. State in detail all operations in performing test. Discuss relative 
accuracy of results. 

8. Test of Platform Scales. 

Apparatus. Platform scales to be tested, 12 in. steel scale, graduated to —^ in. 
and standard 50- or 100-lb. weights. 

Method. Platform scales are probably used more in engineering work about a power 
plant than any other measuring device, and usually young engineers do not very well 
understand their operation. They consist essentially of a device by which a load is 
applied to a system of levers, of long and short arms, arranged so that a load on the 
platform can be balanced by weights applied at the end of a final lever called the beam, 
or by shifting a poise along the length of this latter lever. Essentially it is like the 
weighing device shown in Fig. 370. This weighing beam is usually placed on an upright 
post at one end of the platform. 

1. Take off the platform and measure the length of all the lever arms between knife- 
edges to the nearest y^ in. Draw simple line sketch showing all arms and lengths. 

2. Observe the means provided to adjust the beam to read zero. 

3. Observe sensitiveness of scales by finding range through which poise can be shifted 
without appreciably disturbing the balance. 

4. Calibrate the scales after assembling by placing standard weights on the platform 
and observing the reading on the beam when balanced. After calibration shift scales 
around roughly and observe result by a recalibration. Test also by placing loads in 
middle of platform as a scales should be used, and then at any of the sides. 

Report. 1. Plot results of the calibration with observed weights as abscissas and 
standard weights as ordinates. 

2. Discuss effect of rough handling on the calibration, and whether an accurate 
calibration of a scales made before shipping can be considered absolutely reliable later. 
Explain effect of non-central loading on the platform. 

3. From the measured lever arms calculate the weight of poise for two different 
positions on the beam. 

4. Calculate the weight of a poise for an additional beam which would indicate 
readings to to the smallest division on the beam of this scale. (Note that the additional 
weight of the extra beam could be balanced by a larger adjusting counterweight.) 

9. Oil Tests : Viscosity, Flash and Burning Points, and Specific Gravity. Reference, 
pages 395-404. 

Apparatus. Viscosimeter, flash tester, hydrometer, 2 thermometers, 2 glass gradu- 
ates, Bunsen burner, matches, wax tapers, test-tube, and watch. 

Method. 1. Determine flash and burning points of oil in flash tester, with top closed 
for flash point and open for burning point. To check, use at least two samples of the 
same kind of oil. Never use a second time a sample that has been heated. Why? 
Determine the chill point of the oil if ice is available. 

2. With the orifice of viscosimeter and inner cup thoroughly cleaned determine the 
time required for 50 cu. cm. of water at " room " temperature to flow through this 



OUTLINE OF SUGGESTED TESTS 463 

orifice, starting from the level of the tip of the hook-gage. Make 3 tests and take 
average. Determine similarly the time required for 50 cu. cm. of the oil at temperatures 
of 80, 110, 140 and 170° F. to flow through the same orifice when starting at the same 
level. 

3. Determine the specific gravity of the oil in both the Baume and the " specific 
gravity " scales at about 80°, 100°, 120°, and 140° F. (Avoid pouring hot oils into 
cold glass vessels as they are likely to be broken.) 

Report. Tabulate results of the various tests. Plot (1) temperatures as abscissas 
and viscosities as ordinates, (2) temperatures as abscissas and specific gravity as ordi- 
nates, both curves having the same abscissass on the same sheet. 

Discuss suitableness or unsuitableness of this oil for various services. 

io. Oil Tests (Cont'd) : Coefficient of Friction and Temperature Rise of Bearings. 
Reference, pages 404-405. 

Apparatus. Pendulum oil-tester, thermometer, wooden strut with knife-edge at 
end, sensitive platform scales, spirit level, and steel scale graduated to T £ ff in. 

Method. Support the pendulum in a horizontal position (as determined by a spirit 
level) on a strut, provided with a knife-edge at the bottom where it rests on a platform 
scales. Determine the weight of the pendulum alone in this position. Measure also 
the effective length of the lever arm from the center of the journal to a vertical line 
through the knife-edge. Repeat weighing and measurement of length of arm for 
several points along the pendulum. Remove the pendulum and determine its weight 
accurately. Measure the length (1) and diameter (d) of the journal so as to calculate 

W'R 

the projected area 21d of the bearing surface. Compute the constant , and by 

setting the pendulum at various angles determine whether the scale is correctly gradu- 
ated. In order to get satisfactory results the bearing and shaft must be perfectly clean 
and smooth. Calibrate spring in pendulum. 

Operate the machine at constant speed with pressures of 50, 100, 150 and 200 lbs. per 
sq. in. on the bearing. Record the arc of deflection, temperatures of bearing and of 
room, speed, and rate of oil feed (usually 3 drops per minute). 

Report. Plot curves of bearing pressure (lbs. per sq. in.) as abscissas and coefficient? 
of friction and temperatures as ordinates. 

Calculate velocity of rubbing faces in ft. per min. In machines arranged like ordinary 
shop bearings where all the load is on the bottom half of the bearing this velocity ia 
calculated on the basis of only half the circumference. 

Discuss possible errors in the data as shown by the curves. 

ii. Proximate Analysis of Coal. Reference, pages 228-234. 

Apparatus. Crucibles, Bunsen burners, matches, coal crusher, mortar and pestle, 
20-mesh sieve, 2 air-tight bottles, drying oven, air-blast lamp (or an equivalent), rubber 
tubing, watch, desiccator, and " chemical " balance sensitive to 1 part in 1000 of 
amount weighed. 

Method. That of Am. Chem. Soc. (pages 229-231) or of A.S.M.E. (pages 231-233) 
as directed by instructor. Inquire about location of mine from which coal was taken. 
Make duplicate determinations to check values of moisture and volatile matter. 

Report. Record all data. Determine percentages of moisture, volatile matter, fixed 
carbon and ash in coal " as received." Also percentages of volatile matter, fixed carbon 
and ash in dry coal. Discuss results by comparing with analyses of coals from same 
district as given in mechanical engineers hand-books, etc. 

12. Calorific Value of Coal. Reference, pages 210-222. 

A. Apparatus. Bomb calorimeter with platinum crucible, mortar and pestle, 100- 
mesh sieve, oxygen tank with pipe connections to fit threads on bomb, accurate 



464 POWER PLANT TESTING 

calorimeter, thermometer, pail, 1 scales for weighing water, fine iron wire for ignition, 
" chemical " balance sensitive to 15V0 gram, briquet ting machine, 2 monkey wrench and 
calorimeter spanner. 

B. Apparatus. Same as " A " except Parr calorimeter is used instead of bomb type, 
and absolutely pure sodium peroxide is used instead of oxygen gas. 

Method. See pages 210-215 for " A " and pages 217-219 for " B." Make at least 
two determinations. 

Report for " A " or " B." Describe apparatus used and procedure in detail. Calcu- 
late heating value of coal tested in B.t.u. per lb. " as received," also heating value per 
lb. dry coal and per lb. combustible in same units. Record all data. Discuss results 
by comparing with heating value of coals from same district as given in mechanical 
engineer's hand-books, etc. 

13. Calorific Value of Gas. Reference, pages 222-227. 

Apparatus. Junkers' calorimeter (with gas burner), 2 calorimeter thermometers, 
2 ordinary thermometers, 2 glass graduates, large pail, platform scales, '" wet " gas 
meter, gas regulator, glass U-tube for gas pressure, barometer, and rubber tubing. 

Method. See pages 223-226. Read thermometers every two minutes. 

Make at least two determinations which should check within 1 per cent. 

Report. Tabulate all observations. Explain calculations. 

Determine " higher " and " lower " heating values of the gas per cu. ft. (1) at condi- 
tions of test and (2) at standard conditions (see pages 223). 

Sketch apparatus used. Discuss possible errors in method. 

14. Calorific Value of Oil. Reference, pages 222-227. 

Apparatus. Junkers' calorimeter (with oil lamp and chemical balance for its attach- 
ment) and hydrometer. Otherwise same as for test No. 13. 

Method. See pages 226-227. Collect water from calorimeter during time required 
for burning exactly 50 grams of oil. Determine specific gravity of oil used. Make at 
least two determinations. 

Report. Tabulate all observations. Calculate " higher " and " lower " heating 
values per lb. of oil. Discuss results by comparing with data given in books on gas and 
oil engines or in mechanical engineer's hand-books. 

15. Analysis of Flue Gas. Reference, pages 235-252, 281-283. 

Apparatus for sampling and chemical absorption of gases as directed by instructor. 

Method. See pages 235-245. Make at least two analyses from the same sample of 
gas which should check throughout within T V per cent. 

Report. Tabulate data and results (calculated as percentages). 

From the average results of the analysis calculate number of lbs. air required to burn 
(1) a lb. of carbon and (2) a lb. of dry coal, assuming the dry coal contains 83 per cent 
carbon, 3 per cent hydrogen, 4 per cent oxygen and 10 per cent earthy matter. 

16. Study of Brakes. Reference, pages 147-163. 
Apparatus. Steel scale, calipers, and drawing instruments. 

Method and Report. Design prony brake of type stated by instructor for absorbing 
b.h.p. at. . .r.p.m. Show calculations for diameter at root of thread of tightening bolt, 
and for determining capacity of scales required to take the pressure of the brake. Calcu- 
late also weight of water required per hour for cooling the brake, assuming 10 per cent 
of heat dissipated by radiation. 

Answer the following questions: 

1. If water were shut off from the brake what damage would result? 

1 Instead of the pail and scales a large glass graduate is often used to measure the water 
in cu. cm. 

2 Briquetting the coal is not required by A.S.M.E. recommendations. 



OUTLINE OF SUGGESTED TESTS 465 

2. Why is it a very bad practice to stop the engine with the full load on the brake? 

3. Why should a safety-cord be attached to the arm of the brake? 

4. What is the effect of putting oil on the rim of the brake pulley? Of putting on water? 
If there is any doubt as to the proper answers, run an engine with a Prony brake 

attached to find out by experience. 

17. Calibration of a Transmission Dynamometer. Reference, pages 164-174. 
Apparatus. Dynamometer and its weights steel scale, hand speed counter and watch. 
Method. Measure length of lever arms. Observe condition of dash-pot as explained 

on page 168. Remove the brake from its pulley and make a series of runs; that is, 
without load at various speeds and observe the corresponding readings of instrument. 
Attach the brake to its pulley and make a series of tests at three different speeds with 
net loads on the brake for each speed of approximately (1) . . . (2). . .(3) . . ., and (4) 
. . .lbs. Determine " zero " load or tare of brake, lbs., and length of brake arm, ft. 

For each test record: (1) Gross brake load, lbs., (2) net brake load, lbs., (3) reading 
of dynamometer (theoretically, lbs.), (4) r.p.m., and (5) names of observers. 

Report. Examine construction of dynamometer and sketch arrangement of lever 
arms (and gears, if any). For each speed calculate ft.-lbs. per minute corresponding 
to readings of dynamometer and plot curve with these as abscissas and ft.-lbs. by brake 
as ordinates. Plot also curve for each speed of reading of dynamometer as abscissas 
and net brake load, lbs. as ordinates. 

(For Flather's and Morin's dynamometers plot height of autographic diagram, ins. as 
abscissas with ft.-lbs. by brake as ordinates.) 

18. Belting Tests. Reference, pages 392-394. 

Apparatus. Belt tester, steel tape, 2 hand speed counters, watch, calibrated scales 
for weighing, and 3 ft. scale for lengths. 

Method. See pages 392-394. Determine " zero " load or tare on each scale. Adjust 
the distance between driving and driven pulleys when at rest so that there is initial 
tension in belt of 25 lbs. per in. of width. Run tests at a given constant speed of the 
driver at varying loads until the belt begins to slip. Make about five runs for this value 
of initial belt tension. Each test should be of at least 5 min. duration during which 
time both speed counters should be read continuously. Observe for each test also 
average brake load, lbs. and tension reading, lbs. 

Make similar sets of runs with initial belt tensions of 50 and 75 lbs. per in. of width. 

Measure diameter of either driving or the driven pulleys (inches) and also arc of 
contact of belt on this pulley (inches). Calculate ratio of arc in inches to radius in 
inches. Measure length, width and thickness of belt. 

Report. Calculate slip of belt, coefficient of friction, b.h.p., and efficiency of trans- 
mission. 

For each value of initial tension plot b.h.p. as abscissas and as ordinates (1) slip (per 
cent) and (2) coefficient of friction. Also initial tension of belt as abscissas and b.h.p. as 
ordinates. 

Discuss results in their application to shop practice. 

19. Test of Hoists. Reference, pages 391-392. 

Apparatus. Hoists to be tested, spring balance, scale with graduations marked very 
plainly. 

Method. Same pages as reference. 

Report. Sketch hoists used. On the same curve sheet plot for each hoist a curve of 
load lifted (lbs.) as abscissas and efficiency as ordinates. 

20. Mechanical Efficiency Test of Steam Engine. Determinations of Indicated and 
Brake Horse Power. Reference, pages 136-142, 147, 150, 284. 

Apparatus. Steam engine indicators, steam pressure gage, prony or rope brake, hand 
speed counter, watch, scale about 3 ft. long, platform scales and planimeter, cans of 
cylinder and engine oils. 



466 POWER PLANT TESTING 

Method. Put spring in indicator, oil its piston with cylinder oil and the joints of pencil 
motion with porpoise or similar light oil. Adjust indicator parts so that there is no lost 
motion in pencil mechanism. Attach firmly to engine cylinder. Adjust cord so that 
it will have normal tension when engine is turned over both dead centers. Fill engine 
cylinder lubricator with cylinder oil and all oil cups with engine oil. Adjust feed of all 
oiling devices. Measure effective brake arm and " zero " load or tare of brake (see 
pages 148-151). 

Vary net load on brake by increments of 50 lbs. up to maximum engine will carry 
without slowing down. Run each test for 12 min., taking all indicator cards and read- 
ings of r.p.m. and gross brake reading, lbs. every 3 min. Measure as many indicator 
cards as possible while test is in progress and compare at least a few values of indicated 
with brake h.p. before test is finished. This is done to check the accuracy of the work. 
Always clean the engine and shut off the lubricator and oil cups when finishing a test. 

Calculate engine and brake constants (see pages 143 and 148). 

Report. Tabulate data and calculated results as on page 284. Examine and sketch 
the reducing motion. Explain whether or not it gives an accurate reduction. 

Plot with i.h.p. as abscissas the following as ordinates: (1) b.h.p., (2) mech. effic. 
(per cent), (3) r.p.m. and (4) friction h. p. If friction horse power has not constant values 
discuss reasons. 

21. Setting of Plain D-slide Valve on Steam Engine. Reference, pages 285-288, 289. 
Apparatus. Steel scale, monkey wrench, trammels or large machinist's dividers, 

chalk, drawing-board and instruments and indicators. 

Method. See pages 285-287. Remove steam chest cover and valve from its stem. 
Measure face of valve and ports. Make dimensioned drawing like Fig. 297 (page 285) 
and Zeuner valve diagram. 1 Adjust laps and eccentric as explained in reference. 
Replace steam-chest cover. Attach indicators and take diagrams. Compare with 
ideal diagram obtained from the Zeuner drawing. 

If indicator diagrams are not satisfactory make the adjustments needed. 

Report. Explain in detail procedure. Discuss each step in making adjustments. 

22. Setting of Corliss Valve on Steam Engine. Reference, pages 288-293. 
Apparatus. Monkey wrenches, steel scale, plumb bob and line and indicators. 
Method. Adjust (1) wrist plate, (2) all reach-rods for given laps, (3) rocker. Put 

engine on dead center and set eccentric for a given lead. Readjust reach-rods. Take 
indicator cards and readjust valves. 

23. Volumetric Clearance of Engine. Reference, pages 293-294. 

Apparatus. Pails with cocks near the bottom, rubber tubing, funnels, small platform 
scales for weighing water in pails, trammels, chalk, monkey wrench, watch, wooden 
blocks to cover parts of engine and rubber packing. 

Method. Remove steam-chest cover and cover ports with blocks on top of rubber 
packing. Set engine on dead-center (see page 286, footnote). Continue procedure as 
in reference above. 

24. Boiler Test. Reference, pages 258-283. 

Apparatus. Steam gage, draft gage, barometer, watch, wrenches, steam calorimeter 
(with manometer if needed), thermometers with maximum graduation below 240° F. 
for (1) external air, (2) boiler room, (3) feed-water entering boiler 2 and (4) make-up 
water; above 240° F. for (1) temperature of steam at steam nozzle (discharge from 
boiler) and (2) steam calorimeter, platform scales for (1) coal, (2) ashes and (3) feed- 

1 See treatises on Steam Engines. Zeuner diagrams are most useful for valve setting 
and Bilgram diagrams and best for designing. 

2 For plants operating with an economizer a thermometer for higher temperatures 
would be required. 



OUTLINE OF SUGGESTED TESTS 467 

water, large tanks for feed-water, standard weights, thermo-couple for flue temperature, 
flue gas apparatus for sampling and analyzing, jars or cans for samples of coal and 
ash, means for marking level of water in gage glass, large closed cans for accumulating 
samples of coal and ashes. 

Method. See reference. Calibrate gage and thermometers. Plot a graphical log as 
test proceeds (see page 268). Run boiler leakage test for 3 hrs. at normal boiler 
pressure (see page 339) before regular boiler test begins. 

Report. Tabulate all data. Use A.S.M.E. " short " or " long " form as directed by- 
instructor. 

25. For Economy Tests of Steam Engines, Steam Turbines, Complete Steam Power 
Plants, Gas Engines, Oil Engines, Gas Producers, as well as Pump Tests, Injector 
Tests, Air Compressor Tests, Air Lift Tests, Ventilating Fan Test, and Refrigerating 
Plant Tests. See detailed instructions and A. S. M. E. codes, pages 294-314, 317-328, 
(329-335), 336-340, 345-363,372-376, 386-388, 409-424, 428-430. 

26. Tests of the Strength of Materials of Construction. See Chapter XXIII for 
detailed methods and reports. 



APPENDIX 



Two sets of tables which the author has found useful for " rough 
and ready " calculations are given on the following pages. Table I is 
a short table of the more important properties of saturated steam. 
This table has been taken with permission from Allen and Bursley's 
Heat Engines. 

Table II gives for various common substances the specific gravity, 
density (weight per cubic foot) , specific heat and coefficients of expansion 
per degree Fahrenheit, both linear and volumetric. Coefficient of 
volumetric expansion is three times the linear coefficient of expansion. 



TABLE I 

Properties op Saturated Steam 
english units 



Abs. Pres- 
sure, Pounds 
per Sq. In. 


Tempera- 
ture, De- 
grees F. 


Heat of the 
Liquid. 


Latent 
Heat of 
Evapora- 
tion. 


Total Heat 
of Steam. 


Specific Vol- 
ume, Cu. Ft. 
per Pound. 


Density, 

Pounds per 

Cu. Ft. 


Abs. Pres- 
sure. Pounds 
per Sq. In. 


V 


t 


q or h 


rovL 


H 


v 


l 

V 


V 


.0886 


32 





1072.6 


1072.6 


3301.0 


.000303 


.0886 


.2562 


60 


28.1 


1057.4 


1085.5 


1207.5 


.000828 


.2562 


.5056 


80 


48.1 


1046.6 


1094.7 


635.4 


.001573 


.5056 


1 


101.8 


69.8 


1034.6 


1104.4 


333.00 


.00300 


1 


2 


126.1 


94.1 


1021.4 


1115.5 


173.30 


.00577 


2 


3 


141.5 


109.5 


1012.3 


1121.8 


118.50 


.00845 


3 


4 


153.0 


120.9 


1005.6 


1126.5 


90.50 


.01106 


4 


5 


162.3 


130.2 


1000.2 


1130.4 


73.33 


.01364 


5 


6 


170.1 


138.0 


995.7 


1133.7 


61.89 


.01616 


6 


7 


176.8 


144.8 


991.6 


1136.4 


53.58 


.01867 


7 


8 


182.9 


150.8 


988.0 


1138.8 


47.27 


.02115 


8 



468 



APPENDIX 



469 



Properties op Saturated Steam — Continued 

ENGLISH UNITS 



Abs. Pres- 
sure, Pounds 
per Sq. In. 


Tempera- 
ture, De- 
grees F. 


Heat of the 
Liquid. 


Latent 
Heat of 
Evapora- 
tion. 


Total Heat 
of Steam. 


Specific Vol- 
ume, Cu. Ft. 
per Pound. 


Density, 

Pounds per 

Cu. Ft. 


Abs. Pres- 
sure, Pounds 
per Sq. In. 


V 


t 


q or A 


r or L 


H 


V 


l 


P 


9 


188.3 


156.3 


984.8 


1141.1 


42.36 


.02361 


9 


10 


193.2 


161.2 


981.7 


1142.9 


38.38 


.02606 


10 


11 


197.7 


165.8 


978.9 


1144.7 


35.10 


.02849 


11 


12 


202.0 


170.0 


976.3 


1146.3 


32.38 


.03089 


12 


13 


205.9 


173.9 


973.9 


1147.8 


30.04 


.03329 


13 


14 


209.6 


177.6 


971.6 


1149.2 


28.02 


.03568 


14 


14.7 


212.0 


180.1 


970.0 


1150.1 


26.79 


.03733 


14.7 


15 


213.0 


181.1 


969.4 


1150.5 


26.27 


.03806 


15 


16 


216.3 


184.5 


967.3 


1151.8 


24.77 


.04042 


16 


17 


219.4 


187.7 


965.3 


1153.0 


23.38 


.04277 


17 


18 


222.4 


190.6 


963.4 


1154.0 


22.16 


.04512 


18 


19 


225.2 


193.5 


961.5 


1155.0 


21.07 


.04746 


19 


20 


228.0 


196.2 


959.7 


1155.9 


20.08. 


.04980 


20 


21 


230.6 


198.9 


958.0 


1156.9 


19.18 


.05213 


21 


22 


233.1 


201.4 


956.4 


1157.8 


18.37 


.05445 


22 


23 


235.5 


203.9 


954.8 


1158.7 


17.62 


.05676 


23 


24 


237.8 


206.2 


953.2 


1159.4 


16.93 


.05907 


24 


25 


240.1 


208.5 


951.7 


1160.2 


16.30 


.0614 


25 


26 


242.2 


210.7 


950.3 


1161.0 


15.71 


.0636 


26 


27 


244.4 


212.8 


948.9 


1161.7 


15.18 


.0659 


27 


28 


246.4 


214.9 


947.5 


1162.4 


14.67 


.0682 


28 


29 


248.4 


217.0 


946.1 


1163.1 


14.19 


.0705 


29 


30 


250.3 


218.9 


944.8 


1163.7 


13.74 


.0728 


30 


31 


252.2 


220.8 


943.5 


1164.3 


13.32 


.0751 


31 


32 


254.1 


222.7 


942.2 


1164.9 


12.93 


.0773 


32 


33 


255.8 


224.5 


941.0 


1165.5 


12.57 


.0795 


33 


34 


257.6 


226.3 


939.8 


1166.1 


12.22 


.0818 


34 


35 


259.3 


228.0 


938.6 


1166.6 


11.89 


.0841 


35 


36 


261.0 


229.7 


937.4 


1167.1 


11.58 


.0863 


36 


37 


262.6 


231.4 


936.3 


1167.7 


11.29 


.0886 


37 


38 


264.2 


233.0 


935.2 


1168.2 


11.01 


.0908 


38 


39 


265.8 


234.6 


934.1 


1168.7 


10.74 


.0931 


39 


40 


267.3 


236.2 


933.0 


1169.2 


10.49 


.0953 


40 


41 


268.7 


237.7 


931.9 


1169.6 


10.25 


.0976 


41 


42 


270.2 


239.2 


930.9 


1170.1 


10.02 


.0998 


42 


43 


271.7 


240.6 


929.9 


1170.5 


9.80 


.1020 


43 


44 


273.1 


242.1 


928.9 


1171.0 


9.59 


.1043 


44 


45 


274.5 


243.5 


927.9 


1171.4 


9.39 


.1065 


45 . 


46 


275.8 


244.9 


926.9 


1171.8 


9.20 


.1087 


46 


47 


277.2 


246.2 


926.0 


1172.2 


9.02 


.1109 


47 


48 


278.5 


247.6 


925.0 


1172.6 


8.84 


.1131 


48 


49 


279.8 


248.9 


924.1 


1173.0 


8.67 


.1153 


49 


50 


281.0 


250.2 


923.2 


1173.4 


8.51 


.1175 - 


50 


51 


282.3 


251.5 


922.3 


1173.8 


8.35 


.1197 


51 


52 


283.5 


252,8 


921.4 


1174.2 


8.20 


.1219 


52 


53 


284.7 


254.0 


920.5 


1174.5 


8.05 


.1241 


53 


54 


285.9 


255.2 


919.6 


1174.8 


7.91 


.1263 


54 


55 


287.1 


256.4 


918.7 


1175.1 


7.78 


.1285 


55 


56 


288.2 


257.6 


917.9 


1175.5 


7.65 


.1307 


56 


57 


289.4 


258.8 


917.1 


1175.9 


7.52 


.1329 


57 


58 


290.5 


259.9 


916.2 


1176.1 


7.40 


.1351 


58 


59 


291.6 


261.1 


915.4 


1176.5 


7.28 


.1373 


59 


60 


. 292.7 


262.2 


914.6 


1176.8 


7.17 


.1394 


60 


61 


293.8 


263.3 


913.8 


1177.1 


7.06 


.1416 


61 



470 



POWER PLANT TESTING 

Properties of Saturated Steam — Continued 



ENGLISH UNITS 



Abs. Pres- 
sure, Pounds 
per Sq. In. 


Tempera- 
ture, De- 
grees F. 


Heat of the 
Liquid. 


Latent 
Heat of 

Evapora- 
tion. 


Total Heat 
of Steam. 


Specific Vol- 
ume, Cu. Ft. 
per Pound. 


Density, 

Pounds per 

Cu. Ft. 


Abs. Pres- 
sure, Pounds 
per Sq. In. 


V 


t 


gor h 


. V or L 


H 


* 


V 


V 


62 


294.9 


264.4 


913.0 


1177.4 


6.95 


.1438 


62 


63 


295.9 


265.5 


912.2 


1177.7 


6.85 


.1460 


63 


64 


297.0 


266.5 


911.5 


1178.0 


6.75 


.1482 


64 


65 


298.0 


267.6 


910.7 


1178.3 


6.65 


.1503 


65 


66 


299.0 


268.6 


910.0 


1178.6 


6.56 


.1525 


66 


67 


300.0 


269.7 


909.2 


1178.9 


6.47 


.1547 


67 


68 


301.0 


270.7 


908.4 


1179.1 


6.38 


.1569 


68 


69 


302.0 


271.7 


907.7 


1179.4 


6.29 


.1591 


69 


70 


302.9 


272.7 


906.9 


1179.6 


6.20 


.1612 


70 


71 


303.9 


273.7 


906.2 


1179.9 


6.12 


.1634 


71 


72 


304.8 


274.6 


905.5 - 


1180.1 


6.04 


.1656 


72 


73 


305.8 


275.6 


904.8 


1180.4 


5.96 


.1678 


73 


74 


306.7 


276.6 


904.1 


1180.7 


5.89 


.1699 


74 


75 


307.6 


277.5 


903.4 


1180.9 


5.81 


.1721 


75 


76 


308.5 


278.5 


902.7 


1181.2 


5.74 


.1743 


76 


77 


309.4 


279.4 


902.1 


1181.5 


5.67 


.1764 


77 


78 


310.3 


280.3 


901.4 


1181.7 


5.60 


.1786 


78 


79 


311.2 


281.2 


900.7 


1181.9 


5.54 


.1808 


79 


80 


312.0 


282.1 


900.1 


1182.2 


5.47 


.1829 


80 


81 


312.9 


283.0 


899.4 


1182.4 


5.41 


.1851 


81 


82 


313.8 


283.8 


898.8 


1182.6 


5.34 


.1873 


82 


83 


314.6 


284.7 


898.1 


1182.8 


5.28 


.1894 


83 


84 


315.4 


285.6 


897.5 


1183.1 


5.22 


.1915 


84 


85 


316.3 


286.4 


896.9 


1183.3 


5.16 


.1937 


85 


86 


317.1 


287.3 


896.2 


1183.5 


5.10 


.1959 


86 


87 


317.9 


288.1 


895.6 


1183.7 


5.05 


.1980 


87 


88 


318.7 


288.9 


895.0 


1183.9 


5.00 


.2002 


88 . 


89 


319.5 


289.8 


894.3 


1184.1 


4.94 


.2024 


89 


90 


320.3 


290.6 


893.7 


1184.3 


4.89 


.2045 


90 


91 


321.1 


291.4 


893.1 


1184.5 


4.84 


.2066 


91 


92 


321.8 


292.2 


892.5 


1184.7 


4.79 


.2088 


92 


93 


322.6 


293.0 


891.9 


1184.9 


4.74 


.2110 


93 


94 


323.4 


293.8 


891.3 


1185.1 


4.69 


.2131 


94 


95 


324.1 


294.5 


890.7 


1185.2 


4.65 


.2152 


95 


96 


324.9 


295.3 


890.1 


1185.4 


4.60 


.2173 


96 


97 


325.6 


296.1 


889.5 


1185.6 


4.56 


.2194 


97 


98 


326.4 


296.8 


889.0 


1185.8 


4.51 


.2215 


98 


99 


327.1 


297.6 


888.4 


1186.0 


4.47 


.2237 


99 


100 


327.8 


298.4 


887.8 


1186.2 


4.430 


.2257 


100 


101 


328.6 


299.1 


887.2 


1186.3 


4.389 


.2278 


101 


102 


329.3 


299.8 


886.7 


1186.5 


4.349 


.2299 


102 


103 


330.0 


300.6 


886.1 


1186.7 


4.309 


.2321 


103 


104 


330.7 


301.3 


885.6 


1186.9 


4.270 


.2342 


104 


105 


331.4 


302.0 


885.0 


1187.0 


4.231 


.2364 


105 


106 


332.0 


302.7 


884.5 


1187.2 


4.193 


.2385 


106 


107 


332.7 


303.4 


883.9 


1187.3 


4.156 


.2407 


107 


108 


333.4 


304.1 


883.4 


1187.5 


4.119 


.2428 


108 


109 


334.1 


304.8 


882.8 


1187.6 


4.082 


.2450 


109 


110 


334.8 


305.5 


882.3 


1187.8 


4.047 


.2472 


110 


111 


335.4 


306.2 


881.8 


1188.0 


4.012 


.2493 


111 


112 


336.1 


306.9 


881.2 


1188.1 


3.977 


.2514 


112 


113 


336.8 


307.6 


880.7 


1188.3 


3.944 


.2535 


113 


114 


337.4 


308.3 


880.2 


1188.5 


3.911 


.2557 


114 


114.7 


337.9 


308.8 


879.8 


1188.6 


3.888 


.2572 


114.7 



APPENDIX 



471 



Properties of Saturated Steam 
english units 



Continued 



Abs. Pres- 
sure, Pounds 
per Sq. In. 


Tempera- 
ture, De- 
grees F. 


Heat of the 
Liquid. 


Latent 
Heat of 
Evapora- 
tion. 


Total Heat 
of Steam. 


Specific Vol- 
ume, Cu. Ft. 
per Pound. 


Density, 

Pounds per 

Cu. Ft. 


Abs. Pres- 
sure, Pounds 
per Sq. In. 


V 


t 


qorl 


ror L 


H 


V 


l 

V 


V 


115 


338.1 


309.0 


879.7 


1188.7 


3.878 


.2578 


115 


- 116 


338.7 


309.6 


879.2 


1188.8 


3.846 


.2600 


116 


117 


339.4 


310.3 


878.7 


1189.0 


3.815 


.2621 


117 


118 


340.0 


311.0 


878.2 


1189.2 


3.748 


.2642 


118 


119 


340.6 


311.7 


877.6 


1189.3 


3.754 


.2663 


119 


120 


341.3 


312.3 


877.1 


1189.4 


3.725 


.2684 


120 


121 


341.9 


313.0 


876.6 


1189.6 


3.696 


.2706 


121 


122 


342.5 


313.6 


876.1 


1189.7 


3.667 


.2727 


122 


123 


343.2 


314.3 


875.6 


1189.9 


3.638 


.2749 


123 


124 


343.8 


314.9 


875.1 


1190.0 


3.610 


.2770 


124 


125 


344.4 


315.5 


874.6 


1190.1 


3.582 


.2792 


125 


126 


345.0 


316.2 


874.1 


1190.3 


3.555 


.2813 


126 


127 


345.6 


316.8 


873.7 


1190.5 


3.529 


.2834 


127 


128 


346.2 


317.4 


873.2 


1190.6 


3.503 


.2855 


128 


129 


346.8 


318.0 


872.7 


1190.7 


3.477 


.2876 


'129 


130 


347.4 


318.6 


872.2 


1190.8 


3.452 


.2897 


130 


131 


348.0 


319.3 


871.7 


1191.0 


3.427 


.2918 


131 


132 


348.5 


319.9 


871.2 


1191.1 


3.402 


.2939 


132 


133 


349.1 


320.5 


870.8 


1191.3 


3.378 


.2960 


133 


134 


349.7 


321.0 


870.4 


1191.4 


3.354 


.2981 


134 


135 


350.3 


321.6 


869.9 


1191.5 


3.331 


.3002 


135 


136 


350.8 


322.2 


869.4 


1191.6 


3.308 


.3023 


136 


137 


351.4 


322.8 


868.9 


1191.7 


3.285 


.3044 


137 


138 


352.0 


323.4 


868.4 


1191.8 


3.263 


.3065 


138 


139 


352.5 


324.0 


868.0 


1192.0 


3.241 


.3086 


139 


140 


353.1 


324.5 


867.6 


1192.1 


3.219 


.3107 


140 


141 


353.6 


325.1 


867.1 


1192.2 


3.198 


.3128 


141 


142 


354 ,2 


325.7 


866.6 


1192.3 


3.176 


.3149 


142 


143 


354.7 


326.3 


866.2 


1192.5 


3.155 


.3170 


143 


144 


355.3 


326.8 


865.8 


1192.6 


3.134 


.3191 


144 


145 


355.8 


327.4 


865.3 


1192.7 


3.113 


.3212 


145 


146 


356.3 


327.9 


864.9 


1192.8 


3.093 


.3233 


146 


147 


356.9 


328.5 


864.4 


1192.9 


3.073 


.3254 


147 


148 


357.4 


329.0 


864.0 


1193.0 


3.053 


.3275 


148 


149 


357.9 


329.6 


863.5 


1193.1 


3.033 


.3297 


149 


150 


358.5 


330.1 


863.1 


1193.2 


3.013 


.3319 


150 


152 


359.5 


331.2 


862.3 


1193.5 


2.975 


.3361 


152 


154 


360.5 


332.3 


861.4 


1193.7 


2.939 


.3403 


154 


156 


361.6 


333.4 


860.5 


1193.9 


2.903 


.3445 


156 


158 


362.6 


334.4 


859.7 


1194.1 


2.868 


.3487 


158 


160 


363.6 


335.5 


858.8 


1194.3 


2.834 


.3529 


160 


162 


364.6 


336.6 


858.0 


1194.6 


2.801 


.3570 


162 


164 


365.6 


337.6 


857.2 


1194.8 


2.768 


.3613 


164 


166 


366.5 


338.6 


856.4 


1195.0 


2.736 


.3655 


166 


168 


367.5 


339.6 


855.5 


1195.1 


2.705 


.3697 


168 


170 


368.5 


340.6 


854.7 


1195.3 


2.674 


.3739 


170 


172 


369.4 


341.6 


853.9 


1195.5 


2.644 


.3782 


172 


174 


370.4 


342.5 


853.1 


1195.6 


2.615 


.3824 


174 


176 


371.3 


343.5 


852.3 


1195.8 


2.587 


.3865 


176 


178 


372.2 


344.5 


851.5 


1196.0 


2.560 


.3907 


178 


180 


373.1 


345.4 


850.8 


1196.2 


2.532 


.3949 


180 


182 


374.0 


346.4 


850.0 


1196.4 


2.506 


.3990 


182 


184 


374.9 


347.4 


849.3 


1196.7 


2.480 


.4032 


184 


186 


375.8 


348.3 


848.5 


1196.8 


2.455 


.4074 


186 



472 



POWER PLANT TESTING 



Properties of Saturated Steam — Concluded 

ENGLISH UNITS 



Abs. Pres- 
sure, Pound, 
per Sq. In. 


Tempera- 
ture, De- 
grees F. 


Heat of the 
Liquid. 


Latent 
Heat of 
Evapora- 
tion. 


Total Heat 
of Steam. 


Specific Vol- 
ume, Cu. Ft. 
per Pound. 


Density 

Pound3 

per Cu. Ft. 


Abs. Pres- 
sure, Pounds 
per Sq. In. 


V 


t 


q or h 


rot L 


H 


V 


i 


V 


188 


376.7 


349.2 


847.7 


1196.9 


2.430 


.4115 


188 


190 


377.6 


350.1 


847.0 


1197.1 


2.406 


.4157 


190 


192 


378.5 


351.0 


846.2 


1197.2 


2.381 


.4200 


192 


194 


379.3 


351.9 


845.5 


1197.4 


2.358 


.4242 


194 


196 


380.2 


352.8 


844.8 


1197.6 


2.335 


.4284 


196 


198 


381.0 


353.7 


844.0 


1197.7 


2.312 


.4326 


198 


200 


381.9 


354.6 


843.3 


1197.9 


2.289 


.4370 


200 


202 


382.7 


355.5 


842.6 


1198.1 


2.268 


.4411 


202 


204 


383.5 


356.4 


841.9 


1198.3 


2.246 


.4452 


204 


206 


384.4 


357.2 


841.2 


1198.4 


2.226 


.4493 


206 


208 


385.2 


358.1 


840.5 


1198.6 


2.206 


.4534 


208 


210 


386.0 


358.9 


839.8 


1198.7 


2.186 


.4575 


210 


212 


386.8 


359.8 


839.1 


1198.9 


2.166 


.4618 


212 


214 


387.6 


360.6 


838.4 


1199.0 


2.147 


.4660 


214 


216 


388.4 


361.4 


837.7 


1199.1 


2.127 


.4700 


216 


218 


389.1 


362.3 


837.0 


1199.3 


2.108 


.4744 


218 


220 


389.9 


363.1 


836.4 


1199.5 


2.090 


.4787 


220 


222 


390.7 


363.9 


835.7 


1199.6 


2.072 


.4829 


222 


224 


391.5 


364.7 


835.0 


1199.7 


2.054 


.4870 


224 


226 


392.2 


365.5 


834.3 


1199.8 


2.037 


.4910 


226 


228 


393.0 


366.3 


833.7 


1200.0 


2.020 


.4950 


228 


230 


393.8 


367.1 


833.0 


1200.1 


2.003 


.4992 


230 


232 


394.5 


367.9 


832.3 


1200.2 


1.987 


.503 


232 


234 


395.2 


368.6 


831.7 


1200.3 


1.970 


.507 


234 


236 


396.0 


369.4- 


831.0 


1200.4 


1.954 


.511 


236 


238 


396.7 


370.2 


830.4 


1200.6 


1.938 


.516 


238 


240 


397.4 


371.0 


829.8 


1200.8 


1.923 


.520 


240 


242 


398.2 


371.7 


829.2 


1200.9 


1.907 


.524 


242 


244 


398.9 


372.5 


828.5 


1201.0 


1.892 


.528 


244 


246 


399.6 


373.3 


827.8 


1201.1 


1.877 


.532 


246 


248 


400.3 


374.0 


827.2 


1201.2 


1.862 


.537 


248 


250 


401.1 


374.7 


826.6 


1201.3 


1.848 


.541 


250 


275 


409.6 


383.7 


819.0 


1202.7 


1.684 


.594 


275 


300 


417.5 


392.0 


811.8 


1203.8 


1.547 


.647" 


300 


350 


431.9 


407.4 


798.5 


1205.9 


1.330 


.750 


350 



APPENDIX 



473 



TABLE II 

Properties of Common Substances 



Specif 
Grav- 
ity. 



Weight 

per 
Cubic 
Foot, 
Lbs. 



Weight 
of One 
Cubic 

Inch, 

Lb. 



Specifi. 
Heat. 



Coefficient of Expan- 
sion per Deg. F. 



Volu- 
metric. 



Aluminum 

Bismuth 

Boxwood, along or across grain. 

Brass 

Cement 

Copper 

Coal (anthracite) 

Coke 

Gasoline 

Glass 

Gold... 

Ice (at 32° F.) 

Iron (cast) 

Iron (wrought) 

Lead 

Limestone 

Mercury (at32°F.) 

Nickel 

Pine (white), along grain 

Pine (white), across grain 

Platinum 

Porcelain 

Oak, along grain 

Silver 

Steel 

Tin 

Zinc 



2.60 
9.82 



161 
613 



.095 
.353 



8.10 
2.24 
8.79 
1.43 
1.00 
.68 
2.89 

19.26 
.92 
7.5 
7.74 

11.35 
3.16 

13.60 

8.90 

.55 



503 
140 
545 

88. 

62. 

42. 

180. 

1200 

57. 
465 
582 
708 
197 
849 
547 



.293 
.083 
.318 
.058 
.037 



.105 
.697 
.033 
.271 
.280 
.411 
.114 
.492 
.321 
.020 



21.5 



1342 



.779 



10.47 
7.83 
7.29 
7.19 



653 
486 
452 
445 



.379 
.292 
.264 
.260 



.212 
.031 



.094 

.20 

.097 

.241 

.203 



.000011 

.000008 

.000002 

.00001 

.000008 

.000009 



.000033 

.000024 

.000006 

.00003 

.000024 

.000028 



.198 
.032 
.504 
.130 
.110 
.031 
.217 
.033 
.109 
.65 



.000005 
.000008 



.000014 
.000024 



.000006 
.000007 
.000016 



.000018 
.000021 
.000048 



.032 



.056 
.116 
.056 
.095 



.000033 

.000007 

.0000025 

.000020 

.000005 

.000002 

.000003 

.000011 

.000007 

.000012 

.000016 



.000100 
.000020 
.000008 
.000080 
.000015 
.000006 
.000009 
.000033 
.000020 
.000035 
.000048 



TABLE III 

Metric Conversion Table 



Millimeters X .03937 = inches. 

Millimeters -5- 25.4 = inches. 

Centimeters X .3937 = inches. 

Centimeters -v- 2.54 = inches. 

Meters X 39.37 = inches. (Act of Congress.) 

Meters X 3.281 = feet. 

Meters X 1.094 = yards. 

Kilometers X .6214 = miles. 

Kilometers + 1.6093 = miles. 

Kilometers X 3280.8 = feet. 

Square Millimeters X .00155 = sq. inches. 

Square Millimeters -f- 645.2 = sq. inches. 

Square Centimeters X -155 = sq. inches. 

Square Centimeters -f- 6.452 = sq. inches. 

Square Meters X 10.764 = sq. feet. 

Square Kilometers X 247.1 = acres. 

Hectare X 2.471 = acres. 

Cubic Centimeters -f- 16.387 = cubic inches. 

Cubic Meters X 35.314 = cubic feet. 



474 



POWER PLANT TESTING 



Cubic Meters X 1.308 = cubic yards. 

Cubic Meters X 264.2 = gallons (231 cu. in.) 

Liters X 61.023 = cubic in. (Act of Congress.) 

Liters X .2642 = gallons (231 cu. in.) 

Liters -5- 3.785 = gallons (231 cu. in.) 

Liters 4- 28.317 = cubic feet. 

Hectoliters X 3.531 = cubic feet. 

Hectoliters X 2.838 = bushels (2150.42 cu. in.) 

Hectoliters X .1308 = cubic yards. 

Hectoliters X 26.42 = gallons (231 cu. in.) 

Grams X 15.432 = grains (Act of Congress.) 

Grams X 981. = dynes. 

Grams -r- 28.35 = ounces avoirdupois. 

Grains -r- 15.432 = grams. 

Grains 4- 7000 = pounds. 

Joule X .7373 = foot pounds. 

Kilograms X 2.2046 = pounds. 

Kilograms X 35.27 = ounces avoirdupois. 

Kilograms -r- 907.2 = tons (2,000 lbs.) 

Kilogr. per sq. cent. X 14.223 = lbs. per sq. in. 

Kilogrammeters X 7.233 = foot lbs. 

Kilo per sq. Meter X .672 = lbs. per sq. foot. 

Kilo per Cu. Meter X .0624 = lbs. per cu. ft. 

Kilowatts X 1.34 = Horse Power. 

Watts -T- 746. = Horse Power. 

Watts X .7373 = foot pounds per second. 

Calorie X 3.968 = B.t.u. 

Cheval vapeur X .9863 = Horse Power. 

(Centigrade X 1.8) + 32 = degree Fahrenheit. 

Franc X .193 = Dollars. 

Gravity Paris = 980.94 centimeters per sec. = 32.17 feet per 



TABLE IV 

The Equivalents op Ounces, per Square Inch, in Inches of Height op Columns 
op Water and Mercury 

27.71 inches of water and 2.04 inches of mercury equal one pound per square inch 
at atmospheric pressure and 62° F. Temperature. Mercury is 13.58 times as heavy as 
water. 



Ounces. 


Inches of 
Water. 


Inches of Mercury. 


Ounces. 


Inches of 
Water. 


Inches of Mercury. 


.146 


0.25 


.018 


7 


12.12 


.892 


.292 


0.51 


.037 


8 


13.85 


1.019 


.438 


0.76 


.055 


9 


15.59 


1.148 


.584 


1.01 


.074 


10 


17.32 


1.275 


1 


1.73 


.127 


11 


19.05 


1.402 


2 


3.46 


.255 


12 


20.78 


1.529 


3 


5.20 


.382 


13 


22.52 


1.658 


4 


6.93 


.510 


14 


24.25 


1.785 


5 


8.66 


.637 


15 


25.98 


1.913 


6 


10.39 


.765 


16 


27.71 


2.036 



INDEX 



PAGE 

Absolute Pressure Gages 6 

Absorption Refrigerating Machines 385 

Accelerometer 174 

Air Compressors, Testing of 371-376 

Air Engines , 389 

Air, Flow of 176 

"Air" Horse Power 368, 373 

Air Pump 23 

Air, Velocity and Volume of 180, 369 

Air Supplied to Furnace, Determination of, from Flue Gases 250, 281 

Alden Brake Dynamometer 155 

Allen-Moyer Gas Apparatus 243 

Alternating Current, Measurement of 317, 324 

Ammonia, Leakage of 381 

, Properties of, Tables 380-381 

" Refrigerating Plants 377 

Amsler Planimeter 76 

Analysis of Coal, Proximate 328-333, 463 

Analysis of Flue Gases 235, 464 

Analysis of Fue Gases, Typical Examples of 240 

Anemometers 182 

Aneroid Barometers 6 

Areas, Measurement of 74 

Ash in Fuel, Determination of 230 

Aspirator 236 

Atwater's Fuel Calorimeter " 216 

Averager (Planimeter), Ansler 75-81 

" , Coffin 81-85 

Bachelder Indicator 102-103 

Back-firing Indicator Diagrams 352 

Balance-sheet of Gas Engine . . . 350 

Balance-sheet of Gas Producer 362 

Balance-sheet of Boiler 275, 281, 282 

Balance-sheet of Steam Engine or Steam Turbine 320 

Barometers 4 

" , Corrections for 5 

Barraclough & Mark's Engine Tests 312 

Baume Scale of Specific Gravity 397 

Belts,Testing Tension in 392, 465 

Bending (Transverse) Tests 444 

Blowers, Testing of 364-371 

Boiler Balance-sheet 275, 281, 282 

475 



476 INDEX 

PAGE 

Boiler Efficiency 274, 278 

Boiler Feed-pumps, Testing of 410-417 

Boiler Feed-water, Measurements of, in Tests 273, 319 

Boiler Heat Balance 275, 281, 282 

Boiler Horse Power : 263, 268 

Boiler Summary Sheets 276-281 

Boiler Test Graphical Log Sheet 268 

Boiler Testing: Datum Lines of Water and Fire in Tests 272, 273 

Boiler Testing, Principal Objects of 267 

Boiler Testing, Rules for (A.S.M.E.) 269-281 

Bourdon Pressure Gage, Theory of 7-8 

Bourdon Pressure Gage with Steel Tube 10 

Brake Dynamometers 147-164, 464 

Brake Horse Power 147 

Brake Pulley, Design for 151 

Briquettes of Neat Cement for Testing 447 

Bristol-Durand Integrator for Circular Diagrams 87-91 

Brumbo's Pulley 126 

Burning Point of Oils, How Tested 402, 462 

Calibration of Pressure Gages 15-22, 460 

" Vacuum " ■ 22, 460 

Indicator Springs 112-120, 461 

" Thermo-Electric Thermometers and Pyrometers 45 

" Mercury Thermometers 29-37, 460 

Calorific Value of Fuel, Determination of 210, 463 

Calorific Value of Gas 222, 464 

Calorimeter, Barrel (for Steam) 70 

, Bomb (for Fuels) 211 

, Combined Separating and Throttling 65-69 

, Condensing (Steam) 70 

, Calibration of 73, 461 

, Electric 69 

, Fuel 211-227, 463 

, Junkers 222-227, 464 

, Separating (Steam) 63-65 

, Throttling 55-63 

, Wire-drawing (or Throttling) 55-63 

Charts, for Determining Moisture in Steam 59, 61 

Nipples ' 56, 57, 60, 66 

Capillary Corrections for Mercury 3 

Carbonic Acid (C0 2 ), Apparatus for Determining 240-245, 252 

Carbonic Acid Refrigerating Machine 379 

Cement Tests 447 

Centrifugal Fans,Testing of 364-371 

" Pumps, Testing of 419 

Chemical Analysis of Fuels to Determine Calorific Value 227 

Chill Point of Oils 403 

Chimney Gases, Weight of, Calculated from Analysis 251, 281 

Clearance of an Engine Cylinder, Determination of 293 

Coal Analysis, Proximate 228-233 

Coal, Calorific Value of, from Analysis 227 



INDEX 477 

PAGE 

Coals Recommended for Standard Boiler Trials (A.S.M.E.) 269, 270 

Coal Testing: Proximate Analysis 228, 233, 463 

Coal Calorimeters 211-222, 463 

Coefficient of Dilution 249 

" Discharge for Orifices 186, 189, 191, 202 

" " " Weirs 204 

" " Expansion of Mercury 21 

Coefficients of Expansion of Various Substances Appendix 

" " Friction of Friction Wheels 394 

" " " " Oils and Bearings 404, 463 

Coffin Planimeter 81-85 

Columns, Testing of 442 

Combined Separating and Throttling Calorimeters 65-69 

Commercial Steam Engine Testing 295 

" Turbine Testing 317 

Composimeter 255 

Compound Gages 12 

Compression Tests of Materials 441-442 

Compressors, Air, Testing of 371-376 

" , Ammonia, Testing of 382-385 

Condensers, Testing of 305 

Continuous Indicator 106 

Conversion of Pressures 7 

" Temperatures and Heat Units 29 

Cooley-Hill Continuous Indicator 106 

Cooley Indicator Spring Tester 113-120 

Cooley Stroke Measuring Counter 412 

Corliss Engine Diagrams, Normal and Abnormal 289 

Corliss Engine-Valve setting 288-293 

Correcting Steam Engine and Steam Turbine Tests to Standard Conditions . 329-340 

Correction Curves for a Steam Turbine 329-339 

Correction for Stem Exposure of Mercury Thermometers 36-39 

Crosby Indicator 95-99 

Cups, Thermometer .....:... 30-31 

Curve, Hyperbolic as Applied to Indicator Diagram 298 

" , Typical "Error" 22 

Curves for Determinations of Moisture in Steam 59, 61 

Cut-off, How Determined 288, 298 

Dead-center to Set Engine On 286 

Dead-weight Gage Testers 17-19 

Deflectometers 434 

Density of Water at Different Temperatures 7 

" " Ammonia (Liquid) 380 

" " Substances, Table of Appendix 

Diagram Factor of Engines 303 

Diaphragm Gages 11 

Differential Dynamometer, Calibration of 168 

Gages 12 

Direct Current, Measurement of 323 

Draft Gages 24-27 

Drum Motion Testers 120-122 



478 INDEX 

PAGE 

Ducts, Loss of Velocity in 371 

" , Measuring Velocity of Air in ." 180,369 

Durand-Bristol Integrator 87 

Duty of a Steam Pump 414 

Dynamometer, Alden 155 

" , Differential 165 

" , Dynamo 162 

" , Emerson "Scales" 168 

" , Fan 154 

, Flather 169 

" , Hints on Management 150 

" , Kenerson's 174 

" , Rope and Strap 150-153 

, Torsion 172-175 

, Water Brake 155-162 

" , Webber Transmission 167, 465 

Dynamos as Dynamometers 162 

Eccentric, Setting of, Effect on Indicator Diagram 289 

Econometer 256 

Economy of Steam Engine Compared with Ideal 308 

Eddy Current Brakes 163 

Efficiency of Steam Boiler 274,278 

" " Fans or Blowers 368,373,376 

" " Gas Engine 341,346,350 

" " Gas Producer 357,359 

" " Refrigerating Machines 384,385 

" " Steam Engines, Thermal 305 

" " " Turbines, Thermal 322 

" Compared with Rankine Cycle 322 

Ejector for Flue Gases 236 

Elastic Limit Defined 434 

Electric Dynamometers 162,163 

Electrical Measurement of Power 323 

" Instruments, Precautions to be Observed 324 

" Pyrometers 41-45 

Emerson Fuel Calorimeter 216 

" Power Scales 168 

Engine and Boiler Tests (Combined) 336-340 

Engine Lubricators 405 

Entropy Defined 309 

Entropy-temperature Diagram 309 

Error Curve, Typical 22 

Extensometer 433 

Fan Dynamometers 154-155 

Fans, Ventilating 364 

Feed-water, Measurement of 193-209 

" Thermometer and Gage 53 

Feed Pumps, Testing of 408,410 

Flashing Point of Oil, How Determined 400-403, 462 

Flather's Dynamometer 169 



INDEX 479 

PAGE 

Fliegner's Formula 185 

Flow of Air 176-189, 369 

Steam 189-193 

Water 193-209 

Flue Gas Analysis 235, 464 

Flue Gas, Determination of Air Supply from 250, 281, 283 

Flue Gases, Loss of Heat in 252, 281 

, Weight of 251, 281, 282 

Form for Report of Boiler Test 276 

" " Gas Engine Test 346 

Steam Engine Test 298 

" " " Pump Test 415 

" Turbine Test 325 

Francis Formula for Weirs 204 

Friction Brakes and Dynamometers 147-164 

" Horse Power 284 

Wheels, Tests of 394 

Fuel: Calculation of Heating Value 214, 219, 226, 228 

Fuel Calorimeters 211-227 

Fuel for Gas and Oil Engines, Measurement of 176, 343 

Fuels, Calorific Value of 210 

Fuel Testing 210-234 

Gages, Bourdon 7,8 

, Calibration of 15-22, 460 

, Diaphragm 11 

, Draft 24-27 

, Pressure 7-15 

, Recording 12-15 

, Vacuum 2, 12 

Gage Notch 203, 204 

Gage Testers 17-19 

Gas, Calorific Value of 222 

" , Measurement of 176-189 

Gas Engine Balance Sheet 350 

, Efficiency of 341, 350 

" Fuel, Measurement 343 

" Indicator Diagrams: Normal, "Suction," etc 350, 351 

" showing "Timing" of Ignition 352 

Gas Fuels 353, 464 

" Meters 176 

" Producers 353 

Gasoline, Measurement of 343 

Goss Dynamometer 164 

Goss' Experiments on Indicator Connections 139 

"Guarantee" Tests 321 

Head at a Pump (Suction, Discharge, Total), Defined 409, 414 

Heat Balance of Boiler 281 

Gas Engine 350 

" " Producer 362 

" Refrigerating Plant 384 



480 INDEX 

PAGE 

Heat Units, Conversion of 29 

Heating Value of Fuels Calculated from Analysis 227 

" " by Experiment 211-227 

Heat Unit Basis of Engine Testing 296, 306 

Hempel Gas Apparatus 245-248 

Hirn's Analysis 306 

Hoists, Efficiency of 391, 465 

Hook Gage 203 

Hopkinson's Optical Indicator 112 

Horse Power, Boiler 263, 268 

, Brake 147, 465 

, Indicated 136, 141, 284, 341, 465 

Hot-air Engine, Testing of 389 

Humidity of Air 368 

Hydraulic Machinery, Testing of 408 

Hydraulic Motors, Testing of 419 

Rams, Testing of 424 

Hydrostatic Pressure on Gages 11 

Hyperbolic Curve Applied to Engine Indicator Diagrams 298 

Ice Making Capacity 382 

Ice Melting Capacity 382 

Impellers of Fans 364 

Impulse Water Wheels 424 

Indicated Horse Power, Calculation of 136, 141, 284, 341, 465 

" " Engine Constant 143 

Indicator, Bachelder 102 

, Care of 103 

, Continuous 106 

, Crosby 95 

, Crosby Gas Engine 342 

, High-pressure (Ordnance) 372 

, Optical 108 

, "Star Brass" 99 

, Tabor- 99 

, Thompson 93 

, Watt 92 

Indicator Diagrams, Analysis of 136-141 

" , Calculation of Steam Consumption from 297, 304, 310, 312 

" from Flather's Dynamometer 170-171 

of Gas and Oil Engines 350-352 

" showing Back Firing 352 

" of Suction Stroke 350 

" Taken with Light Spring Attachment 350 

Indicator Drum Testing Apparatus 120-122 

Spring Testing " 112-120 

" , Calibration of 112, 460 

Injector, Method of Operating 428 

Testing 428 

" Test, Form for Report on 429 

" Used in Boiler Testing, Correction Applied to Feed- Water 271 

Integating Instruments, Durand-Bristol 87 



INDEX 481 

PAGE 

Integrating Instruments, Planimeters 75-91 

"Internal" Horse Power 321 

Junkers Gas Calorimeter 222-227, 464 

Kenerson's Torsion Dynamometer , 174 

Latent Heat of Ammonia 381 

Steam, Table of Appendix 

Leakage Test of a Boiler 259, 319, 339 

of Steam in Tests 260, 305 

Light Spring Indicator Diagrams of Suction Stroke of Gas Engine 350 

Log Form for Indicator Spring Test 119 

" for Mechanical Efficiency Test of Engine 284 

" for Pressure Gage Test 21 

" for Thermometer Calibration 34, 37 

Losses of Head in Ducts 371 

Low Pressure Gages 22 

Lower Heat Value of Gas 224-226 

Lubricators, Engine 405-407 

Lubricants, Tests of 395-407 

Mahler Bomb Calorimeter 21 1-214 

Machines for Testing Strength of Materials 431-450 

Manograph 110-112 

Manometers 1-4 

Mean Ordinate, Determination of 80, 83, 142 

" Effective Pressure by Coffin Planimeter -83 

Mechanical Pyrometer 45 

Efficiency 284, 341, 371, 385, 465 

Mercury Columns, Cleaning of 7 

" " , Corrections for 3 

" , and Equivalent Pressure per Unit Area 7 

" Column for Calibrating Gages 19-23 

" Expansion of 21 and Appendix 

" Thermometers 28 

Metallic Pyrometers 45 

Meter, Gas 176-178 

" , Venturi 199 

Metric Conversion Table 471 

Modulus of Elasticity 434 

Moisture in Coal 229, 232 

" " Steam (by Charts) , 58-61 

" " " , Determination of 55 

Moulds for Cement Briquettes 448-450 

Napier's Formula 189 

Oil Engines, Measurement of Fuel for '. 343 

Oils, Tests of 395-407, 462 

"Orsat" Apparatus 241-245 

Optical Indicators 108-113 

Optical Pyrometers 50 



482 INDEX 

PAGE 

Pantograph Reducing Motion for Indicators 121, 124, 127 

Parallel Rule for Dividing Diagrams 142 

Parr Calorimeters 217 

Pendulum Reducing Motions 125 

Permanent "Set" Defined 434 

Perry Optical Indicator 108-109 

Pitot Tubes 178-182 

Planimeter, Amsler 76 

, Calibration of 86, 460 

, Coffin 81 

" , Polar, Theory of 76 

" , Roller 85 

Platform Scales 260, 462 

Pneumatic Pyrometers 46 

Polar Planimeter 75 

Positive Pressure Blowers 366 

Power, Measurement of 147 

Power Scales, Emerson 168 

Pressure (lbs. per square inch) and Equivalent Head of Water or of Air 7, 474 

Pressure and Temperature of Steam, Table of Appendix 

Pressure Type of Gas Producer 353 

Pressure Gages 7-16 

" , for Measuring Draft 24 

" , Calibration of 15-23 

" , Recording' 12-15 

Pressure Gage Tester, Dead-weight 17 

Pressure Scales, Crosby" 18, 19 

Prony Brake 147, 464 

Proximate Analysis of Coal 228-233, 463 

Pulsometer, Testing of 426 

Pump, Centrifugal, Testing of 419 

Pumping Engine Trials 413-419 

Pumps, Effective Head at (footnote) 409 

" , Testing of Feed 411 

Pyrometer, Calibration of 45 

Calorimeter 51 

" Cones 52 

" , Electric Resistance 44 

" , Mechanical 45 

" , Mercury 40, 46, 53 

, Optical 50 

" , Radiation 47-50 

, Recording 39-41, 47 

" , Thermo-electric 41-44 

Quality of Steam, How Calculated 58, 68, 70, 72 

" Determined from Charts 59, 61 

Radiation Loss in Calorimeters 64, 67, 68, 211, 214, 221 

Rankine Cycle Steam Engines and Turbines 304, 308, 322 

Ratings of Capacity, Commercial 266 

Ratio of Expansion 298 



INDEX 483 

PAGE 

Reaction Water Turbines 422 

Recording C0 2 Apparatus 252-255 

" Gages 12-15 

" Thermometers 37-41 

" Pyrometers 37-41, 47 

Reducing Motions for Indicators 121-136, 461 

Refrigerating Plants 377 

" Capacity 382 

Report of Boiler Test, Forms For 276 

" Gas Engine Test, Forms for 346 

" Steam Engine Test, Forms for 298 

" " Turbine Test, Forms for 325 

Resilience 435 

Revolution Counters 144 

Rider Hot Air Engine 389 

Rope Brake 151, 464 

" , Hints on Management of (footnote) 150 

Rope Drives, Tension in 392 

Rotary Engine, Indicated h. p 143 

Rules for Boiler Testing (A.S.M.E.) 269 

Gas Engine Testing (A.S.M.E.) 345 

Steam Engine Testing (A.S.M.E.) 294 

" Turbine Testing (A.S.M.E.) 325 

Sampling Bottle for Flue Gases 235-240 

Sampling Coal 228, 231 

Tubes for Flue Gas (A.S.M.E.) 238, 272 

Scales -for Weighing Fuel 260, 462 

Seger Pyrometer Cones 51 

Separating Calorimeter 63 

" Set" (Permanent) Defined 434 

Shaft Dynamometers 172, 175 

Simpson's Rule for Areas 74 

Siphons for Steam Gages 9-10 

Sirocco Fans 364 

Slip in Pumps 409, 413 

Smallwood's Drum Motion Tester 121-122 

Smoke Observations 225, 274 

Specific Gravity Determinations 395, 451 

Specific Gravities of Various Substances, Table of Appendix 

Specific Heat of Ammonia 381 

" " Various Substances, Table of Appendix 

" " Superheated Steam 309, 310 

" Volume of Steam Appendix 

Speed Counters 144, 146 

Speed-output Curves 316, 322 

Spring Tester, Indicator 112-120 

Standard Conditions for Ventilating Fans(U. S. Navy) 370 

" " Engine and Turbine Tests 329 

" " Gases 223, 226, 357 

Steam, Flow of 189 

Steam Calorimeters 55-73, 461 



484 INDEX 

PAGE 

Steam Consumption Calculated from Indicator Diagram 297, 304 ,310, 312 

" Determined from Feed-water 296, 319, 339 

when using Surface Condenser 295, 305 

" Calculated from Heat Balance 319, 320 

" Engine Lubricators 405 

" " Testing, Rules for 294 

" " Thermal Efficiency of 305 

Steam Measurement (Meters, etc.) 189-193 

" , Tables of Properties of 34, 468 

Stem Exposure of Thermometers, Correction for 36-39 

Stroke-measuring Counter 412 

Suction Gas Producer, Testing of 353 

" Stroke Diagrams of a Gas Engine 350 

" Head of Pump, Measurement of with Gage (footnote) 409 

Superheated Ammonia 381 

" Steam, Flow of 189 

" " , Specific Heat of 309 

Surface Condensers, Testing of 305 

Tabor Indicator 99 

Tachometers 145 

Temperature, Measurement of 28 

" Scales, Conversion of 29 

Tension Tests of Materials 435, 437 

Testing Boilers 267 

" Gas Engines 341 

" Hydraulic Motors 419-426 

" Impulse Water Wheels 419 

" Refrigerating Machines 377 

" Steam Engines 284, 294 

" " Pumps 413 

" Turbines 315 

" Strength of Materials 431 

" Ventilating Fans and Blowers 364 

" Water Turbines 422 

Test-pieces, Standard Shapes and Sizes for 436,448 

Theoretical Water Rate 322 

Thermal Efficiency of a Gas Engine 350 

" " Steam Engine 297, 304, 305 

" " " Turbine 322, 328 

Thermo-electric Pyrometers and Thermometers 41-44 

Thermometer, Alcohol 29 

" and Pressure Gage Combined 53 

, Calibration of 29, 31-37, 460 

" Correction for Stem Exposure 36-39 

for Flue Gases 28, 41-54 

" for High Temperatures 28, 46 

, Mercury 28-38, 40, 46, 53 

" , Recording 39-41 

" with Mercury Well for Steam Pipes 53-54 

" , Regraduating of (footnote) 28 

' , Standard 31 



INDEX 485 

PAGE 

Thermometer, Thermo-electric 41-44 

Wells 30-31 

, Wet and Dry Bulb 368-369 

Thompson Indicator 93-94 

Throttling Calorimeters 55 

Timing of Ignition 352 

Torque (footnote) 147 

of Steam Turbine 322 

Torsion Dynamometers 172-175 

Total Heat of Saturated Steam, Table of Appendix 

" " Superheated Steam 296 

Trammels, Method of, for Setting Engine on Dead Center (footnote) 286 

Transmission Dynamometers 164-175, 465 

Transverse Bending Tests 444 

Turbine Dynamometer, Westinghouse 158 

Two-fluid Manometers (Draft Gages) : 26-27 

Ultimate Strength Defined 435 

U-tube Manometers 1-4, 6, 24, 26 

Vacuum Gages, 2, 12 

on Suction Pipes of Pumps (footnote) 409 

Valve Setting, D-slide and Piston Types ■. 285-288 

Corliss Type 288-293 

Velocity of Air 178-183, 367 

Ventilating Fans 364-367 

R ; ij " Systems, Testing of 366 

Venturi Water Meter 199 

Vicat Needle 453 

Viscosity 398, 462 

Volatile Matter in Coal 230, 232 

Volume of Air Discharged by a Blower ' 368 

" of a Pound of Steam, Table of Appendix 

Volumetric Efficiency of Refrigerating Machine 383 

Water Brakes 155-162 

" Cooled Brake Pulley 150-151 

" Equivalent of Calorimeters 72, 210 

" Flow through Circular Orifice or Nozzle 201-203 

" Friction Djmamometer, Westinghouse 158-161 

" Measurement of by Weir 203-207 

" , Measuring Tank, Continuous 196-198, 207-209 

" Meters 193-206 

" Meter, Venturi 199 

" Rate Curve 316 

" Rate, Theoretical ' 322 

" Seals for Pressure Gages 9-10 

" Turbines 422 

" , Weight of at Different Temperatures 7 

" Wheels, Testing of *. 419 

Watt's Indicator 92-93 

Weak Spring Indicator Diagrams 350 



486 INDEX 

PAGE 

Webber's Transmission Dynamometer 167 

Webb's Viscous Dynamometer 161-162 

Weighing Machine for Water 196-199, 205 

Weight of Air Required to Burn a Pound of Fuel 250, 281-283 

Weight of Air, Table of 181 

" Chimney Gases 251, 281 

" Flue Gases 251, 281 

" a Cubic Foot of Steam, Table of Appendix 

" Various Substances, Table of Appendix 

" Water at Different Temperatures 7 

Wells, Thermometer 30-31 

Westinghouse Water Brakes 158-161 

Wet and Dry Bulb Thermometer for Humidity 368-369 

Willans Law 312 

" Lines ; . • 313-315 

Willcox Water Weigher 196 

Wire-drawing Calorimeters (Throttling) 55 



